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A COMPLETE 


ENCYCLOPEDIA OF ELECTRICITY 


I. A Book of Useful Tables and Practical Hints for Elec¬ 
tricians, Foremen, Salesmen, Estimators, Contractors, 
Architects and Engineers. 

II. Practical Diagrams and Descriptions for all Kinds of 
Electrical Construction Work. 

III. Direct and Alternating Current Motors, Showing Prin¬ 
ciples, Construction, Operation and Maintenance. 

IV. Operating and Testing Manual, for Men in Charge of 
Electrical Apparatus, Repair Men, Trouble Men, Lamp 
Trimmers and Electricians Generally. 


BY 

DAVID PENN MORETON 
HENRY C. HORSTMANN 
VICTOR H. TOUSLEY 


FULL Y ILLUSTRA TED 


Published Exclusively for 

SEARS ROEBUCK & COMPANY 

by 

FREDERICK J. DRAKE & CO. 
CHICAGO 
1921 









Copyright 1921, 1919 and 1917 
By 

Frederick J. Drake & Co. 


MAR 22 1321 



§>CI.A6ii262 



I 


ELECTRICAL 
TABLES AND DATA 























■ 
























. 



































































ELECTRICAL TABLES AND 
ENGINEERING DATA 


Acid Fumes. —In places where acid fumes or cor¬ 
rosive vapors may exist, the nature of the vapors 
will determine the insulation to be used. Consult 
chemists and Inspection Department having juris¬ 
diction. Conduit w T ork is not favored much in such 
places, but if it can be shown that the vapors in 
question are not harmful to the metal it is permissi¬ 
ble. 

Adapters. —There is no objection to the use of 
adapters, provided they are of approved type. 

Adjusters. —The use of cord adjusters should be 
discouraged, but there is no very serious objection to 
the use of any that do not severely damage the cord. 

Air Compressors. —Air compressors are usually 
driven by series wound motors and made to stop 
and start automatically. For a. c. work induction 
motors are used. Tanks should be of a capacity 
equal to about 50 per cent of the rated capacity of 
the compressor per minute. The air should be dry 
and cool, as most of the moisture will be precipi¬ 
tated. One H.P. will compress about 5^ cu. ft. of 
free air per minute to 90 lbs. 

Alternating Current Wiring. —For alternating cur¬ 
rent systems the two or more wires must be run in 
the same metal conduit, armored cable or metal 
moulding. In open wiring the greater the separa¬ 
tion of wires, the greater will be the inductive drop. 



8 


ELECTRICAL TABLES AND DATA 


See also special tables for sizes of motor wires and 
wiring systems. 

Alternators. —Alternating current generators and 
their exciters are not usually provided with fuse 
protection. 

Aluminum. —Aluminum is used as a rule only for 
outside work and for bus-bars. It can be soldered, 
but soldering is more difficult than with copper wire 
and clamps are therefore much used. When used 
for bus-bars the current density ranges from 1,000 
to 1,200 amperes per sq. in. for the smaller sizes, and 
about 500 for the heavy bars. See Bus-Bars for 
table. For insulated aluminum wire the safe carry¬ 
ing capacity is 84 per cent of that given for copper 
wire of same insulation. Aluminum is electroposi¬ 
tive and must be tied with aluminum wire and no 
other metal must be allowed to touch it. 

Comparison of Copper and Aluminum: 


Aluminum 


Specific gravity. 2.68 

Eelative specific gravity. 1.00 

Conductivity .61 to 63 

Weight for equal area. 47 

Area for equal conductivity. 160 


Diameter for equal conductivity. 126 


Copper 
8.93 
3.33 
96 to 99 
100 
100 
100 


It will be noted that an aluminum wire of equal 
conductivity is about two sizes larger by B. & S. 
gauge than a copper wire. The tensile strength of 
aluminum is from 20,000 to 35,000 pounds per square 
inch; that of copper from 20,000 to 65,000. For 
carrying capacity, etc., see Wire Calculations. 

Ammeters. —It is customary to provide an ammeter 
for each generator connected to a switchboard, and 
only the very smallest and cheapest boards are ever 
put up without one. The cord sent out with shunt 
ammeters must always be used full length and need 
not be protected by fuses. Never place an ammeter 







ELECTRICAL TABLES AND DATA 


9 


in any lead that can be affected by equalizer current. 
An ammeter used for battery charging should indi¬ 
cate direction of current. 

Ampere’s Rule. —Imagine yourself swimming with 
the current and facing the center of the coil; the 
left hand will then point toward the north pole of 
the magnet. 

Anode. —The anode is the positive pole. 

Annunciators. —Unless the annunciator is known 
to be especially constructed for high voltage, no at¬ 
tempt should be made to operate it from light or 
power circuits. Use bell ringing transformers, mo¬ 
tor generators or battery. Annunciators cannot be 
operated in parallel successfully. 

Apartment Buildings. —If practicable, meters 
should be placed in basement. In some cities spe¬ 
cial rules for the wiring of apartment buildings ex¬ 
ist. No cut-outs should ever be placed in closets; 
place them in kitchen if possible. To determine ap¬ 
proximate size of mains necessary to supply lighting 
in apartment buildings, estimate one watt per square 
foot and consult table of carrying capacities. 

Arcades. —The illumination of arcades should be 
kept low so as not to interfere with show windows. 

Arc Lamps. —In laying out wiring for arc lamps 
the question of drop need not be considered unless 
incandescent lamps are also on the circuit. A wire * 
smaller than No. 6 should not be used for theatre, or 
moving picture arc lamps. Two dissolving stereop- 
ticon lamps are usually rated as about equal to one 
stage or moving picture arc lamp. 

Plugs used for arc and incandescent lamps should 
not be interchangeable. The light from direct cur¬ 
rent arc lamps is much better than that from alter¬ 
nating current. Series arc lamps are now operated 
almost entirely from constant current transformers; 
each transformer being limited to one circuit. 


Arc Lamp Data 


10 


ELECTRICAL TABLES AND DATA 


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ELECTRICAL TABLES AND DATA 


11 


Armored Cable and Cord. —Armored conductors 
are very suitable for “fish work.” The radius of 
the curve of the inner edge of any bend must not be 
less than iy 2 inches. Where moisture exists the con¬ 
ductors should be lead-covered under the armor. Ar¬ 
mored cable is not nail proof under all circumstances. 

TABLE I 

Outside Diameters of Armored Cables and Weight Per 100 Ft. 
Greenfield Flexible. Steel Armored Conductors 


B&S 

Single conductors, type D. .14 

12 

10 

8 

6 


Twin conductors, BX.14 

12 

10 

Three conductors, BX3....14 

12 

10 

Single conductors, DL. 

Lead covered, and steel 
armored . 


Twin conductors, BXL....14 
Steel armored and lead 12 

covered .Id 

Three conductors, BXL3...14 
Lead covered and steel 12 

armored .10 

Steel armored, flexible 
cord, Type E. 


Steel armored, flexible re¬ 
inforced cord, Type EM. 


Solid 


Stranded 

Dia. 

Wt. 


Dia. 

Wt. 

in. 

lbs. B&S 

in. 

lbs. 

.378 

20 

10 

.450 

23 

.384 

21$ 

8 

.469 

28 

.434 

26 

6 

.631 

54 

.464 

28 

4 

.717 

63 

.609 

54 

2 

.783 

71 



1 

.900 

98 

.630 

45 

8 

.830 

77 i 

.670 

48 

6 

1.116 

121 

.720 

54 

4 

1.203 

143 

.675 

53 

8 

.890 

93 

.715 

56$ 

6 

1.144 

153 

.785 

66 

10 

.506 

53 



8 

.564 

72 



6 

.713 

95 



4 

.780 

110 



2 

.825 

125 • 



1 

.897 

165 

.730 

68 

8 

.978 

136 

.758 

78 

.6 

1.152 

205 

.863 

110 




.782 

78 

8 

1.056 

164 

.815 

97 




.933 

129 

18 

.414 

20 



16 

.447 

22 



14 

.625 

38 



18 

.530 

25 



16 

.540 

26 



14 

.652 

48 








12 


ELECTRICAL TABLES AND DATA 


Armory.—Armories are often classed with thea< 
tres and assembly halls, and must be wired accord¬ 
ingly. The most important part of an armory is the 
drill hall. This requires an illumination equal to 
about two or two and one-half foot candles. This 
is best obtained by placing large units high up out 
of the range of vision. 

Artists.—Require an adjustable light and pendant 
drops are most serviceable. 

Art Gallery. —Art galleries are also often classed 
with assembly halls. In illuminating statuary, the 
aim must be to produce some shadow effect because 
of the uniformity of color. Lights should be hung 
high. For white statuary an illumination of two- 
foot candles will be sufficient; for bronze statuary 
about four times as much should be provided. Paint¬ 
ings are often illuminated by strips and reflectors, 
and also by indirect lighting or Holophane globes. 
As many paintings must be viewed from a distance, 
a bright illumination of about five foot candles is 
recommended. 

Asbestos. —This becomes a conductor when wet, 
and must not be used in damp places. Asbestos less 
than -J inch thick is not considered serviceable. As¬ 
bestos covered wires are much used for connecting 
arc lamps and rheostats where the wdre is subject to 
much heat. 

Assembly Halls. —The National Electrical Code 
prescribes that if any part of a building is “regu¬ 
larly or frequently used for dramatic, operatic, 
moving picture, or other performances or shows, or 
has a stage used for such performances used with 
scenery or other stage appliances,” it must be classed 
as a theatre, and wired according to theatre rules. 
It is usual to specify that all wires must be in con¬ 
duit and that there must be a separate system of 
lighting, independent of the main system, for use of 


ELECTRICAL TABLES AND DATA 13 

the audience in leaving the building in case of fire, 
or other emergency. 

Attachment Plugs.— Must be of approved type. 
They should be of the pull-out type, and the socket 
so placed that the plug can pull out in case strain is 
put upon it. 

Automatic Cut-outs are required to protect every 
device, or wire, which is connected to any power 
circuit, except alternators and constant current 
generators. For details see Cut-outs. 

Automobiles. —In wiring automobiles it is custom¬ 
ary to disregard all ordinary construction rules. 
Electric motors are connected without any fuse pro¬ 
tection. A fuse blowing on a heavy up-grade might 
cause disaster. 

Auto-Starters. —As a general rule, auto-starters are 
not used with motors smaller than 5 H.P. Auto 
starters provided with overload release devices, and 
so arranged that the handle cannot be left in the 
starting position, are obtainable and should be used. 
Small auto-starters have usually three taps, and these 
are arranged to give about 50, 65 or 80 per cent of 
the line voltage. Larger starters usually have four 
taps arranged respectively for 40, 58, 70 and 80 per 
cent of the line voltage. Always make connections 
to the lowest voltage tap that will give the necessary 
starting torque. Wherever possible, place starter in 
sight of motor. For motors smaller than 5 H.P., 
throw-over switches are often used. 

Bakeries. —In bakeries, hot places will be found in 
which rubber-covered wire is not suitable. 

Balance Sets. —Balance sets are made up of motor 
generators or transformers, and exist for the pur¬ 
pose of obtaining a neutral wire and low voltage 
for a small lighting load operated in connection with 
a higher voltage two-wire generator. They are also 
used where motors operate at two voltages. The 


14 


ELECTRICAL TABLES AND DATA 


capacity of a balancing set is usually only a small 
percentage of the total load. 

Balancing. —Three-wire systems are usually ar¬ 
ranged so that a minimum of current may pass 
through the neutral wire. A good balance cannot 
alwavs be obtained, and in some cases considerable 
judgment is required to determine which is the best 
arrangement of apparatus. Three wires should be 
carried to every center supplying more than one 
circuit. Safety rules require the neutral wire to be 
of same size as the outside wire, but in large systems 
this wire will seldom be called upon to carry more 
than 10 per cent of the current used at any time. 

Ball Rooms. —Ball rooms are often classed with 
theatres. The illumination should be general, and 
lamps hung high. A general illumination of from 
two to four foot candles is recommended. Recep¬ 
tacles for musicians’ use should be provided. 

Banana Cellars. —These places are always hot and 
moist and the vapors are very corrosive. Conduits 
corrode very fast, and especially the small screws 
in outlet boxes; brass screws are often used. Open 
wiring, if it can be protected, is preferable. 

Banks. —In that part of a bank occupied by the 
clerical force, a general illumination of from three 
to four foot candles is recommended. These lights 
are in use most of the time, and high efficiency lamps 
should be arranged for. In that portion used by the 
public the illumination is not so much used, and 
may be of a lower order. Numerous outlets for 
adding machines and fan motors should be provided. 
In some banks the private depositors’ rooms are 
fitted with two lights, one above and one below 
desks, and provided with three-way switches so that 
only one light can be used at a time; this for con¬ 
venience of customers who may have dropped things 
on the floor. 


ELECTRICAL TABLES AND DATA 


15 


Barber Shops. —Good illumination of barber shops 
can be arranged for by placing clusters of fairly 
large candlepower close to the ceiling and a little 
to the rear of chairs. Placed in this manner, the 
light will not be forced directly into the line of 
vision of the customer, and yet give the desired 
illumination. The mirrors in front of chairs will 
reflect much of the light back to the chair. Often 
lights are placed along the mirrors, but this practice 
is not to be recommended. Outlets for cigar-lighters, 
curling-iron heaters, vibrators, etc., will be appre¬ 
ciated. 

Bams. —The use of brass shell sockets should be 
avoided in horse barns. Avoid placing lights in 
front of horses, and keep all lights well up above 
horses’ heads. Use weatherproof construction in 
wash rooms. Place lights in all dark comers. 

Bases. —All electrical contacts must be mounted on 
non-combustible, non-absorbtive insulating material. 
Other materials than slate, marble, or porcelain are 
not favored much, and are allowed only when the 
first named are too brittle. Sub-bases are generally 
provided for all switches and other devices which 
would otherwise allow the wires to come against 
wood or plaster. 

Base Frames. —Base frames are required under all 
generators and motors, and where the voltage is not 
in excess of 550 volts it is customary to use insulated 
base frames. If the motor operates at a voltage in 
excess of 550, it is better to ground the frame thor¬ 
oughly. Where frames cannot be insulated they 
must be grounded. 

Basements. —Basements are often damp, and must 
then be wired in accordance with rules for such 
places. As ceilings are usually low, protection 
against mechanical injury is often necessary. 


16 


ELECTRICAL TABLES AND DATA 


Batteries, Primary. —Dry batteries are much used 
at the present time. They require no attention and 
when worn out are simply thrown away. The dry 
battery is at present made only for open circuit 
work. The wet battery used mostly for open circuit 
work consists of carbon and zinc elements immersed 
in a solution of sal-ammoniac. The carbon is the 
positive pole. This battery is charged by dissolving 
about four ounces of sal-ammoniac in sufficient water 
to fill the jar about three-fourths full. Never use 
more sal-ammoniac than will readily dissolve. It is 
preferable to make a saturated solution and, after 
filtering it through cloth, to add about 10 per cent 
of water. Keep jars in a cool place to prevent evapo¬ 
ration. Never allow water to freeze. Keep exposed 
parts covered with paraffine. Do not allow battery 
to be short circuited or run down. If this has oc¬ 
curred, it will often pick up if left on open circuit 
for a few hours. If the solution appears milky, 
more sal-ammoniac is required. Impure zincs which 
do not eat away evenly facilitate the formation of 
crystals which greatly increase the resistance. The 
best known of the closed circuit batteries is the 
gravity type. The elements in this cell are zinc and 
copper, immersed in a solution of sulphate of copper 
(blue vitriol). The copper element rests on the bot¬ 
tom of the jar, and the blue vitriol is placed around 
it and the jar filled with clean water. The cell must 
be short circuited for a few hours to start the action. 
The blue solution should rise to about midway be¬ 
tween the two elements. This cell must be kept in 
action or it will rapidly deteriorate. 

Connect all batteries so that the resistance of the 
battery is nearest equal to the resistance of the de¬ 
vices it is to operate. Series connection should be 
used when the external resistance is higher than the 
internal battery resistance. If the external resist- 


ELECTRICAL TABLES AND DATA 


17 


ance is lower than that of the battery, group cells 
in multiple. When arranging small storage batteries 
to be charged from lighting or power circuits, pro¬ 
vide double throw switches to entirely disconnect 
battery from power circuit while it is on the bell 
circuit. Install all wiring subject to power voltage 
in accordance with rules for that voltage. • 

Batteries, Secondary.—Small storage batteries 
may be carried about and used. The larger ones 
must remain stationary and are used as compensa¬ 
tors for feeder drop, equalizers on three-wire sys¬ 
tems, preventives against shut down and as a com¬ 
bination of all of these. Medium size storage 
batteries are also much used with automobiles. All 
storage batteries with exception of the Edison, use 
lead plates. The active material is sponge lead im¬ 
mersed in a weak solution of sulphuric acid. The 
positive plates when fully charged are of a chocolate 
color and the active material is quite solid. The 
negative plate is more of a slate color and softer. 
The unit of capacity is the ampere hour. A 60- 
ampere-hour battery, for instance, can deliver a cur¬ 
rent of three amperes for twenty hours, or seven 
and one-half amperes for eight hours. High voltages 
are obtained by connecting a number of cells in 
series. High amperage is obtained by connecting 
plates in parallel. The voltage is independent of 
the size of the cell, but the amperage capacity varies 
w T ith the surface of the opposed plates. The effi¬ 
ciency is roughly about 75 per cent. The safe rate 
of charge and discharge varies from five to ten am¬ 
peres per square foot of positive plate surface, both 
sides of plate being measured. The voltage should 
never be allowed to fall below 1.8, and when fully 
charged is about 2.6. The condition of full charge 
is indicated by both the positive and negative plates 
gassing freely. 


18 


ELECTRICAL TABLES AND DATA 


Before manipulating or attempting to connect any 
storage battery, the instructions of the maker should 
be obtained. The following instructions form only 
a general guide: Keep electrolyte well above plates. 
See that the cells are kept clean and allow nothing 
that could short-circuit the plates to accumulate at 
the bottom. Keep whatever separators there may be 
in place. Allow no metal except lead in the battery 
room. Insulate cells from ground and from each 
other. See that battery is recharged as soon as pos¬ 
sible after being used. Do not overcharge. When 
the negative plates begin to give off gas, it is time 
to quit. Never allow the voltage to fall below 1.75 
per cell. The temperature of the battery should not 
rise above 110 degrees. The capacity of battery 
needed is governed by number of units in the gen¬ 
erating plant. It is not likely that more than one 
unit will give out at a time. 

Bells. —Bell-ringing transformers are much used in 
connection with alternating current in place of bat¬ 
teries. To operate bells in series, jump circuit 
breaker on all but one. If bells are to be operated 
from lighting circuits, the wiring must be installed 
in accordance with rules for the voltage used, and 
the bell must be specially approved for that service. 
The chief hazard that exists with low voltage bell 
wires is the possibility of coming in contact with 
other wires. If storage batteries of high amperage 
capacity are used, the wires should have fuse 
protection. 

Belting.—Figure 1 is an illustration of a service¬ 
able method of belt lacing. Thread lacing from left 
to right according to heavy lines, double up at ends 
and return to starting point; cross lacing on out' 
side of belt only, and keep laces on inside parallel 
with length of belt. 


ELECTRICAL TABLES AND DATA 19 

Holes should be punched as nearly as possible 
according to the following table: 


TABLE II 
Width of Belt 


2 to 

Distance from edge of belt— 6 in. 

First row. 4 

First row. I 

Second row. | 

Second row. 1 

Distance apart of each row of holes 1 
Size of lace leather.^ 


6 to 12 to 18 to 

12 in. 18 in. 24 in. 

I | 1 

$ 4 1 

1 14 14 

14 14 2 

14 14 2 

4 ft 4 


If pulleys are of same size, or far apart if of 
different sizes, the length of belt can be quite approx¬ 
imately found by the following rule: Add diameters 



Figure 1.—Method of Belt Lacing. 


of pulleys and multiply by 1.57; to this add 2 times 
the center-to-center distance. The length of belting 
contained in a roll can be found by reference to 
Table III. Multiply number of layers in roll by 
number found where outside diameter of roll and 
diameter of hole in center cross. 

Example.—A roll of belting of 48 inches outside 
diameter has a hole in the center six inches in diam- 












20 


ELECTRICAL TABLES AND DATA 


eter, and there are 88 layers of belting. Where the 
line pertaining to 48 inches outside diameter crosses 
the line pertaining to 6-inch hole, we find the num¬ 
ber 7.04, which multiplied by 88 gives 619.52 feet 
of belting. The width of a single belt necessary to 
perform a certain amount of work can be found by 
the formula W = 1200 x H.P. -r V, where W stands for 
width, H.P. for horsepower, and V for velocity of 
belt in feet per minute. This formula will give a 
belt of ample size, and a smaller one can be made 
to do the work by giving it greater tension. Table 
IV is calculated from the above formula and shows 
the capacity of belts of various widths and operating 
at various velocities. 

Belts should run horizontally and the pull should 
be on the under side. Tightener should be on slack 
side and close to main pulley. Belts running ver¬ 
tically must be kept very tight, especially if the 
lower pulley is small. The proportion between two 
pulleys close together should not be greater than 
6 to 1. Double belting should not be used on pulleys 
less than 3 feet in diameter. Rubber belting is pref¬ 
erable in damp places. Thin belting is best for high 
speeds. Belts operating at high speeds should be 
cemented, not laced. Pulleys should be perfectly 
smooth. 

Billboards.—A very bright illumination of from 
ten to twenty foot candles is often used. Lights 
must be encased in reflectors so as not to be visible 
to the observer. Install wiring according to rules 
for outside work. 

Billiard Halls. —A general illumination of about 
one foot candle is recommended. Above each table 
there should be an illumination of four or five-foot 
candles. The light over the table should be uniform. 
At least two lamps should be provided for each 
table, and should be so encased that the lights are 


ELECTRICAL TABLES AND DATA 


21 


TABLE III 


Table for Calculating Length of Belting, Hope or Wire in Coils 


Outside /-Diameter of Hole in Inches 


Diameter 2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

6 

in. 

. .1.05 

1.17 

1.30 

1.44 








7 

in. 

. .1.17 

1.31 

1.44 

1.57 

1.70 







8 

in. 

. .1.31 

1.44 

1.57 

1.70 

1.83 

1.96 






9 

in. 

.. 1.44 

1.57 

1.70 

1.83 

1.96 

2.09 

2.23 





10 

in. 

.. 1.57 

1.70 

1.83 

1.96 

2.09 

2.23 

2.46 

2.49 




11 

in. 

..1.70 

1.83 

1.96 

2.09 

2.23 

2.36 

2.49 

2.62 

2.75 



12 

in. 

..1.83 

1.96 

2.09 

2.23 

2.36 

2.49 

2.62 

2.75 

2.88 

3.01 


13 

in. 

. .1.96 

2.09 

2.23 

2.36 

2.49 

2.62 

2.75 

2.88 

3.01 

3.14 

3.27 

14 

in. 

..2.09 

2.23 

2.36 

2.49 

2.62 

2.75 

2.S8 

3.01 

3.14 

3.27 

3.40 

15 

in. 

. .2.23 

2.36 

2.49 

2.62 

2.75 

2.88 

3.01 

3.14 

3.27 

3.40 

3.53 

16 

in. 

. .2.36 

2.49 

2.62 

2.75 

2.88 

3.01 

3.14 

3.27 

3.40 

3.53 

3.66 

17 

in. 

. .2.49 

2.62 

2.75 

2.88 

3.01 

3.14 

3.27 

3.40 

3.53 

3.66 

3.79 

18 

in. 

. .2.62 

2.75 

2.88 

3.01 

3.14 

3.27 

3.40 

3.53 

3.66 

3.79 

3.92 

19 

in. 

. .2.75 

2.88 

3.01 

3.14 

3.27 

3.40 

3.53 

3.66 

3.79 

3.92 

4.06 

20 

in. 

. .2.88 

3.01 

3.14 

3.27 

3.40 

3.53 

3.66 

3.79 

3.93 

4.06 

4.19 

22 

in. 

. .3.14 

3.27 

3.40 

3.53 

3.66 

3.79 

3.92 

4.05 

4.19 

4.32 

4.45 

24 

in. 

..3.40 

3.53 

3.66 

3.79 

3.92 

4.05 

4.19 

4.31 

4.45 

4.58 

4.72 

26 

in. 

. .3.66 

3.79 

3.92 

4.05 

4.18 

4.31 

4.45 

4.57 

4.71 

4.84 

4.97 

28 

in. 

..3.92 

4.05 

4.18 

4.31 

4.44 

4.57 

4.71 

4.83 

4.98 

5.11 

5.24 

30 

in. 

. .4.18 

4.31 

4.44 

4.57 

4.70 

4.83 

4.98 

5.09 

5.23 

5.36 

5.50 

32 

in. 

. .4.44 

4.57 

4.70 

4.83 

4.96 

5.09 

5.24 

5.35 

5.49 

5.62 

5.75 

34 

in. 

..4.70 

4.83 

4.96 

5.09 

5.22 

5.35 

5.50 

5.62 

5.75 

5.88 

6.01 

36 

in. 

. .4.96 

5.09 

5.22 

5.35 

5.48 

5.67 

5.76 

5.88 

6.02 

6.15 

6.28 

38 

in. 

..5.22 

5.35 

5.48 

5.61 

5.74 

5.88 

6.02 

6.14 

6.28 

6.41 

6.54 

40 

in. 

..5.48 

5.61 

5.74 

5.87 

6.00 

6.14 

6.28 

6.41 

6.57 

6.68 

6.82 

42 

in. 

..5.74 

5.87 

6.00 

6.13 

6.26 

6.40 

6.54 

6.67 

6.81 

6.94 

7.08 

44 

in. 

. .6.00 

6.13 

6.26 

6.39 

6.52 

6.66 

6.80 

6.93 

7.07 

7.20 

7.34 

46 

in. 

..6.26 

6.39 

6.52 

6.65 

6.78 

6.92 

7.06 

7.19 

7.33 

7.46 

7.60 

48 

in. 

..6.52 

6.65 

6.78 

6.91 

7.04 

7.18 

7.32 

7.45 

7.56 

7.72 

7.86 


This table may also be used to estimate length of 
rope or wires in coils if number of turns can be 
determined. 




22 


ELECTRICAL TABLES AND DATA 


TABLE IV 


The table below is calculated from the above formula and 
shows the number of H. P. belts will transmit 


Belt Speed 


Per Min. 

— 

Width of Belt m Inches 


1 


1 

2 

9 

u 

4 

5 

6 

7 

8 

9 

10 

200 

... .16 

.33 

.50 

.66 

.83 

1.00 

1.16 

1.33 

1.50 

1.66 

300 

... .25 

.50 

.75 

1.00 

1.25 

1.50 

1.75 

2.00 

2.25 

2.50 

400 

... .33 

.66 

1.00 

1.32 

1.66 

2.00 

2.33 

2.66 

3.00 

3.32 

500 

... .42 

.84 

1.25 

1.67 

2.10 

2.50 

2.95 

3.34 

3.75 

4.20 

600 

... .50 

1.00 

1.50 

2.00 

2.50 

3.00 

3.50 

4.00 

4.50 

5.00 

700 

... .58 

1.14 

1.75 

2.33 

2.90 

3.42 

4.08 

4.67 

5.25 

5.80 

800 

... .67 

1.34 

2.01 

2.66 

3.34 

4.02 

4.67 

5.33 

6.00 

6.68 

900 

... .75 

1.50 

2.25 

3.00 

3.75 

4.50 

5.25 

6.00 

6.75 

7.50 

1000 

... .83 

1.66 

2.49 

3.33 

4.15 

4.98 

5.83 

6.66 

7.50 

8.30 

1200 

.. .1.00 

2.00 

3.00 

4.00 

5.00 

6.00 

7.00 

8.00 

9.00 10.0 

1400 

...1.16 

2.32 

3.50 

4.67 

5.80 

7.00 

8.13 

9.34 10.5 

11.6 

1600 

.. .1.33 

2.66 

4.00 

5.33 

6.66 

8.00 

9.33 10.6 

12.0 

13.3 

1800 

...1.50 

3.00 

4.50 

6.00 

7.50 

9.00 10.5 

12.0 

13.5 

15.0 

2000 

. . .1.67 

3.34 

5.00 

6.67 

8.36 10.0 

11.7 

13.4 

15.0 

16.7 

2200 

...1.83 

3.66 

5.50 

7.32 

9.15 11.0 

12.8 

14.6 

16.5 

18.3 

2400 

. ..2.00 

4.00 

6.00 

8.00 10.0 

12.0 

14.0 

16.0 

18.0 

20.0 

2600 

. ..2.16 

4.32 

6.50 

8.66 10.8 

13.0 

15.1 

17.3 

19.5 

21.6 

2800 

...2.33 

4.66 

7.00 

9.33 11.6 

14.0 

16.3 

18.6 

21.0 

23.2 

3000 

. . .2.50 

5.00 

7.50 10.0 

12.5 

15.0 

17.5 

20.0 

22.5 

25.0 

3200 

. . .2.66 

5.32 

8.00 10.6 

13.3 

16.0 

18.6 

21.2 

24.0 

26.7 

3400 

. . .2.83 

5.66 

8.50 11.3 

14.1 

17.0 

19.8 

22.6 

25.5 

28.2 

3600 

. . .3.00 

6.00 

9.00 12.0 

15.0 

18.0 

21.0 

24.0 

27.0 

30.0 

3800 

. ..3.16 

6.32 

9.50 12.6 

15.8 

19.0 

22.1 

25.2 

28.5 

31.6 

4000 

... 3.33 

6.66 10.0 

13.3 

16.6 

20.0 

23.3 

26.6 

30.0 

33.2 

4200 

.. .3.50 

7.00 10.5 

14.0 

17.5 

21.0 

24.5 

28.0 

31.5 

35.0 

4400 

.. .3.67 

7.34 11.0 

14.6 

18.3 

22.0 

25.6 

29.2 

33.0 

36.6 

4600 

. . .3.83 

7.66 11.5 

15.3 

19.1 

23.0 

26.8 

30.6 

34.5 

38.2 

4800 

. . .4.00 

8.00 12.0 

16.0 

20.0 

24.0 

28.0 

32.0 

36.0 

40.0 

5000 

...4.17 

8.34 12.5 

16.7 

20.9 

25.0 

29.2 

33.4 

37.5 

41.8 









ELECTRICAL TABLES AND DATA 


23 


TABLE V 

Table showing approximate lengths of material which must 
be cut out of belts to double the tension; sag on upper and 
lower sides assumed equal. Reducing sag by one-half ap¬ 
proximately doubles the tension. 


Distance Between 
Pulley Centers 

in Feet /-Dimensions Below in 64th of an Inch 


4—Sag ... 

...31 

46 

62 

77 

92 

108 

123 

138 

154 

Cutout 

• • • • • 

2 

3 

5 

7 

10 

13 

17 

20 

6—Sag ... 

...46 

69 

92 

115 

138 

161 

184 

207 

231 

Cutout 

... 1 

3 

5 

7 

11 

15 

19 

25 

30 

8—Sag ... 

...62 

92 

123 

154 

185 

216 

246 

277 

308 

Cutout 

... 1 

4 

6 

10 

15 

20 

26 

33 

41 

10—Sag .., 

.... 77 

115 

154 

192 

230 

269 

307 

346 

384 

Cutout 

... 1 

4 

8 

12 

18 

25 

32 

41 

50 

12—Sag ... 

...92 

138 

184 

230 

276 

322 

368 

415 

462 

Cutout 

... 2 

5 

9 

14 

21 

29 

38 

49 

59 

15—Sag .. . 

.. .115 

173 

231 

288 

345 

402 

459 

518 

577 

Cutout 

... 2 

7 

12 

18 

28 

37 

48 

62 

76 

18—Sag ... 

...138 

207 

277 

346 

415 

485 

554 

623 

693 

Cutout 

... 3 

8 

14 

22 

33 

44 

58 

74 

91 

21—Sag ... 

...161 

242 

323 

404 

485 

566 

647 

727 

807 

Cutout 

... 3 

9 

16 

26 

39 

51 

70 

87 

106 

25—Sag ... 

...192 

288 

384 

480 

576 

672 

768 

864 

960 

Cutout 

... 4 

12 

19 

31 

46 

61 

81 

104 

127 

30—Sag .. . 

...231 

346 

461 

576 

691 

806 

921 

1036 

1151 

Cutout 

... 4 

14 

23 

37 

55 

74 

97 

124 

152 


The above table is based upon the ratio of deflec¬ 
tion and elongation of wires in spans, and it is 
assumed that the additional strain produces no 
immediate elongation of the belt. 














24 


ELECTRICAL TABLES AND DATA 


not visible to the players. A switch for each table 
will be a convenience. Outlets for cigar-lighters 
and fan motors should be provided. 

Bonds. —Rail bonds should not be smaller than 
No. 000. The area of contact should be about eight 
times the cross section of the bond. In some in¬ 
stances the size of bond is determined by the size of 
supply wires, the total cross section of all bonds at 
any point being made equal to the cross section of 
the supply wires for that point. For a ratio of 1:12 
the copper in circular mils necessary to equal the 
conductivity of steel rails can be found by multiply¬ 
ing the weight per yard of rail by 10,000. 

Boosters,—Boosters may be in the form of trans¬ 
formers or motor generators, and are used to raise 
or lower voltage, also in some cases in return rail¬ 
way circuits to lessen electrolysis. The installation 
of boosters is not profitable except on long lines 
when the cost of copper to prevent the drop is 
greater than the cost of boosters. Boosters may be 
compounded so that the regulation becomes auto¬ 
matic. 

Bowling Alleys. —The illumination should be ar¬ 
ranged so that no light is visible to the players. An 
illumination equal to one and one-half or two foot 
candles is advisable for the alley, and about double 
that much for the pins. 

Branch. Blocks must always provide double pole 
fuse protection for each circuit. 

Branch Circuits. —The term, “branch circuit,” is 
here used to describe that part of the wiring between 
the last fuse and the lights, motors, heaters, or other 
translating devices. Branch circuits should be 
grouped as far as possible and arranged so that the 
cut-out cabinet may be in a safe and convenient 
place. It is advisable to place the switches outside 
of cut-out cabinets. In the best arranged theatres 


ELECTRICAL TABLES AND DATA 25 

all branch circuits, except those for emergency 
lights, are carried to stage switchboards. By run¬ 
ning mains as far as possible, and shortening the 
branch circuits, a much evener voltage at lamps will 
be secured than is possible from long branch cir¬ 
cuits. The drop in voltage should never be over 2 
per cent. Most lamps are marked for three voltages, 
top, middle, and bottom, and there is a difference of 
four volts between them. With a 4 per cent drop a 
110-volt lamp will be at different times subject to all 
three voltages and the illumination will vary greatly. 

For best location of cut-outs, see table on calcu¬ 
lation of materials. The following table shows drop 
in voltage with different wires at different distances. 
A run of No. 14 wire 110 feet long feeding twelve 
lights evenly spaced ten feet apart will cause a drop 
of about one and one-quarter volts between first and 
last lamps. The table below shows the drop with 
wires from No. 14 to 6, carrying six amperes the 
distances given at top of table. 

TABLE VI 


Distance in feet; one leg 


& s 

20 

40 

60 

80 

100 

120 

140 

160 

180 

200 

14 .. 

.63 

1.3 

1.9 

2.5 

3.2 

3.8 

4.4 

5.0 

5.7 

6.3 

12 .. 

.40 

.80 

1.2 

1.6 

2.0 

2.4 

2.8 

3.2 

3.6 

4.0 

10 .. 

.25 

.50 

.75 

1.0 

1.3 

1.5 

1.8 

2.0 

2.3 

2.5 

8 .. 

.15 

.30 

.45 

.60 

.75 

.90 

1.1 

1.2 

1.4 

1.5 

6 .. 

.10 

.20 

.30 

.40 

.50 

.60 

.70 

.80 

.90 

1.0 


Burglar Alarm. —A good burglar alarm is one 
so wired that it is under constant test, so as to give 
immediate notice when any part of it is out of order. 
The closed circuit system complies with this require¬ 
ment. With open circuit systems it is best to pro¬ 
vide “silent test” by which it can be tried out every 
night without causing an alarm. To guard against 
purposive incapacitating, some installations are 


26 


ELECTRICAL TABLES AND DATA 


mixed open and closed circuit system, so that it is 
impossible to know which wire to cut or short-circuit 
in order to prevent an alarm. In some systems 
balanced ” relays are used and the wires are inter¬ 
woven so that it is impossible to interfere with them 
in any way without giving an alarm. Where either 
the simple open or closed circuit system is used, the 
wires and batteries should be protected against inter¬ 
ference. 

Bus-Bars.—The term, “ bus-bar, ” refers, strictly 
speaking, only to those conductors on a switchboard 
which are connected directly to all of the machines. 
In common practice, however, it is understood that 
all of the current-carrying bars on a switchboard 
come under this classification. For high voltages it 
is usual to cover the bars with insulation, but for low 
voltages it is customary to leave them bare. The 
proper separation of bus-bars is 2 \ inches for volt¬ 
ages less than 300, and 4 inches for the higher, in¬ 
cluding 550 volts. Copper and aluminum are used. 
Systematize bus-bars by placing all positive poles at 
top or right-hand side of circuit. A current density 
of 1000 amperes per square inch is common practice 
for bus-bars, but is too high for the large ones. 

Table number VII shows the current-carrying 
capacity of bus-bars calculated on a basis of 1000 
amperes per square inch cross section. For very 
small bars 1^ times as much current may be allowed, 
while for the very large ones not more than half the 
current given in the table should be used. The carry¬ 
ing capacity of aluminum is given as 84 per cent of 
that of copper. 

Bushings. —In connection with very high voltages, 
specially constructed bushings must be used through 
walls. Ordinary bushings cause trouble. If possible 
the wires should be run in without touching any¬ 
thing. 


ELECTRICAL TABLES AND DATA 


27 


Thick¬ 

Width 

TABLE VII 

Table of Bus-Bar Data 

Area in Lbs. Per Foot 

Carrying Capacity 
840 

1000 Amperes 
Amp. Per Sq. In. 
Per Sa. In. Alumi- 

ness 

Sq. in. 

Copper 

Aluminum 

Copper 

num 

A 

£ 

.0313 

.1205 

.0361 

32 

27 

A 

£ 

.0469 

.1807 

.0542 

47 

39 

A 

1 

.0625 

.2410 

.0723 

63 

53 

A 

l£ 

.0938 

.3615 

.1084 

95 

80 

i 

£ 

.0625 

.2410 

.0723 

63 

53 

£ 

£ 

.0938 

.3615 

1084 

95 

80 

* 

l 

.1250 

.4820 

.1446 

125 

105 

£ 

l£ 

.1875 

.7230 

.2169 

188 

158 

£ 

2 

.2500 

.9640 

.2892 

250 

210 

I 

£ 

.1875 

.7230 

.2169 

188 

158 

£ 

l 

.2500 

.9640 

.2892 

250 

210 

£ 

1£ 

.3125 

1.205 

.3615 

315 

265 

£ 

H 

.3750 

1.446 

.4338 

375 

315 

£ 

i£ 

.4375 

1.687 

.5061 

435 

365 

£ 

2 

.5000 

1.928 

.5784 

500 

420 

£ 

2£ 

.5625 

2.169 

.6507 

565 

475 

£ 

2£ 

.6250 

2.410 

.7230 

625 

530 

£ 

£ 

.3750 

1.446 

.4338 

375 

310 

£ 

l 

.5000 

1.928 

.5784 

500 

420 

£ 

l£ 

.6250 

2.410 

.7230 

625 

525 

£ 

l£ 

.7500 

2.892 

.8676 

750 

630 

£ 

if 

.8750 

3.374 

1.1122 

875 

735 

£ 

2 

1.000 

3.856 

1.1568 

1000 

840 

£ 

2£ 

1.125 

4.338 

1.3014 

1125 

995 

£ 

2£ 

1.250 

4.820 

1.4460 

1250 

1050 

£ 

2£ 

1.375 

5.304 

1.5912 

1375 

1155 

£ 

3 

1.500 

5.784 

1.7352 

1500 

1260 

£ 

3£ 

1.625 

6.266 

1.8798 

1625 

1365 

£ 

3£ 

1.750 

6.748 

2.0244 

1750 

1470 

£ 

3£ 

1.875 

7.230 

2.1690 

1875 

1575 

£ 

4 

2.000 

7.712 

2.3136 

2000 

1680 

£ 

1 

.750 

2.892 

.8676 

750 

630 

£ 

1£ 

1.125 

4.338 

1.3014 

1125 

945 

£ 

2 

1.500 

5.784 

1.7352 

1500 

1260 

£ 

2£ 

1.875 

7.230 

2.1690 

1875 

1575 

£ 

3 

2.250 

8.676 

2.6118 

2250 

1890 

£ 

3£ 

2.625 

10.122 

3.0366 

2625 

2260 

£ 

4 

3.000 

11.568 

3.4704 

3000 

2520 


28 


ELECTRICAL TABLES AND DATA 


The Aluminum Company of America recommends 
1200 amperes per square inch for the smaller bars 
and 500 for the largest. 

Cabinets.—Metal cabinets only are used in con¬ 
nection with conduit systems. Cabinets are obtain¬ 
able in four thicknesses of steel, viz., 16, 14, 12, and 
10 U. S. Standard gauge, equal to 1/16, 5/64, 7/64, 
and 9/64 inches respectively. The thin metal is used 
only for the smaller boxes, and the heavy for the 
large ones. The depth of cabinets is usually great 
enough to allow door to close with small switches 
in any position, and the large ones thrown way 
back. For necessary dimensions, see Cut-outs, Panel 
Boards, or Switches. Where conduits enter all from 
one end, a wiring gutter space equivalent to about 
4 square inch for each circuit of number 14 twin 
conductor should be allowed. Cabinets should be 
provided to enclose all cut-outs. If practicable, 
locate them so as to reduce likelihood of rubbish 
being stored in them to a minimum. To locate 
switches outside of cut-out cabinets is good practice. 
In ordering cabinets note the following points: Wood 
or metal. Wall or flush mounting. With or without 
lining. With or without wiring gutter. Thickness 
of steel desired. Over-all dimensions of cut-outs, 
panel board, or switch. Inches of back wiring 
pocket. Inches of side wiring pocket.' Spring hinges 
or not. Type of handle or lock. Side on which 
hinge must be. Finish and nature of door. 

Candle Power.—This term is rather loosely used 
and has no very definite meaning, unless qualified 
by one of the following terms: Apparent candle 
power; equivalent candle power; mean lower hemi¬ 
spherical candle power; mean horizontal candle 
power; maximum candle power. The candle power 
of no lamp is the same in all directions. 


ELECTRICAL TABLES AND DATA 


29 


Canopies. —The number of lamps to be used for 
the illumination of outlines in canopies is usually 
governed by the design of the canopy. The best 
effect, where outline lighting is to be installed, is 
obtained from many small lamps of low intrinsic 
brilliancy. Keep lamps and sockets out of the 
weather. Fixture canopies must be insulated wher¬ 
ever an insulating joint is called for on fixture. 

Carbons. —For life of carbons with various types 
of arc lamps, see Arc Lamps. The upper carbon is 
usually the positive, and for projecting arcs is larger 
than the lower. The positive carbon holds its heat 
longer than the negative. If carbons are too large, 
the arc will travel around them. With direct cur¬ 
rent, the upper or positive carbon is consumed twice 
as fast as the other. Flaming arc carbons contain 
special materials in the core, and the color of the 
arc is governed by this material. 

Car Houses. —A main switch is usually provided 
by which all wires in the car house can be cut off. 
Where a car house contains many sections it is better 
to provide a switch for each section. The illumina¬ 
tion of car houses is usually by series incandescent 
lighting. 

Carriage Calls. —These are usually made up in the 
form of electric signs, and located above canopies 
of theatres and hotels. They consist of a large num¬ 
ber of monograms and require a large number of 
wires to be run to them. Outdoor wires should be 
run in water-tight conduit system. If armored cable 
is used outdoors it must be lead-covered insulation. 

Cathode. —The cathode is the negative pole. This 
term is used in connection with batteries and electro¬ 
lytic devices, mostly. 

Ceiling Fans. —These must never be fastened 
rigidly, but in such a manner as to allow them to 
find their own “centers” when running. Not more 


30 


ELECTRICAL TABLES AND DATA 


than 660 watts may be connected to one circuit. 
One fan to 400 or 500 square feet floor space is com¬ 
mon practice. 

Celluloid is highly inflammable, and must never 
be used exposed to heat or flame. Where a trans¬ 
parent medium of a similar appearance is needed, 
gelatine is used. 

Cement when wet is a good conductor and may 
easily cause grounds. 

Centers of Distribution. —In most cases the loca¬ 
tion of centers is governed by other conditions than 
economy of copper, and is dictated by the desire of 
the user. Where, however, free choice of location 
is given, the following tabulation showing the rela¬ 
tive number of circular mils for each branch cir¬ 
cuit of 660 watts at 110 volts will be of use. The 
table shows that with small mains, and especially 
three-wire systems, the amount of copper in the 
mains may be much less than in the branch circuits, 
and that it will be more profitable to run mains into 
the area to be served. This advantage grows less 
with larger mains. Branch* circuits require 8214 
circular mils per circuit of 660 watts. 

The theoretical requirements per 660 watts for 
mains supplying centers is given below: 


Mains B. & S. 

TABLE VIII 

2 Wire 

3 Wire 

14 

3286 

2460 

12 

3957 

2968 

10 

5000 

3752 

8 

5693 

4270 

6 

6325 

4744 

5 

7227 

5426 

4 

7200 

5397 

3 

7914 

5934 


Chandeliers. —No part of any chandelier should be 
less than six feet two inches above floor. The usual 


ELECTRICAL TABLES AND DATA 


31 


height ranges between this and seven feet. In thea¬ 
tres and similar places where chandeliers hang very 
high, arrangement should be made for either raising 
or lowering to admit of lamp renewals. For large 
chandeliers special permission to use 1320-watt cir¬ 
cuits can usually be obtained. 

Chemical Works.—Before undertaking work in 
such places, investigate the nature of fumes, and 
chemicals used, with reference to effect upon copper 
and insulating materials, especially metal conduits, 
if considered. 

Choke Coils. —These are used mostly in connec¬ 
tion with lightning arresters. They must be as well 
insulated as the circuit wires to which they are 
connected. 

Churches. —Some of the large churches require a 
lighting equipment similar to that of theatres. In 
choir lofts and at altars, pockets for special lights 
are often required. Indirect lighting is very useful 
in churches, as the light should be kept out of the 
line of vision of the speaker as well as the audience. 
From two to three foot candles are necessary. Emer¬ 
gency lighting should also be provided. 

Circuit Breakers are much more sensitive than 
fuses. Many of them are so constructed as to allow 
a considerable overload for a short time, and the 
length of this time is adjustable. Circuit breakers 
should ordinarily not be set more than 30 per cent 
above the rated carrying capacity of the wire they 
are to protect. 

Coils. —The coils of a magnet must be connected 
so as to form a continuous spiral. 

Coloring Lamps. —Coloring and frosting of lamps 
reduces the light from 30 to 50 per cent. Amber 
coloring reduces the light about 20 per cent, while 
green and red take up from 50 to 90 per cent, 
according to the density and shade. Prepared color- 


32 


ELECTRICAL TABLES AND DATA 


ing materials can be had at all supply stores. A few 
amber-colored lamps are sometimes mixed in with 
white lights to give a warmer glow to the light. 


Color of Light Sources.— 

Moore tube (carbon dioxide gas).White 

Intensified arc .White 

Magnetite arc .White 

Open arc .Nearly white 

Tungsten lamp .Nearly white 

Tungsten lamp, gas-filled.White 

Nernst lamp .Nearly white 

Enclosed arc (short arc).Bluish white 

Tantalum lamp .Pale yellowish white 

Gem lamp .Pale yellowish white 

Carbon lamp.Pale yellowish white 

Regenerative flame arc.Yellow 

Flaming arc.Variable with different carbons 

Mercury lamp (glass tube).Bluish green 

Enclosed arc (long arc).Bluish white to violet 

High sun.White 

Low sun.Orange red 

Skylight .Bluish white 

Welsbach mantle .Greenish white 

Common gas burner.Pale orange yellow 

Kerosene lamp .Pale orange yellow 

Candle .Orange yellow 


TABLEIX 

Comparison of Fahrenheit and Centigrade Thermometers 


Fah. 

Cent. 

Fah. 

Cent. 

Fah. 

Cent. 

Fah. 

Cent. 

Fah. 

Cent. 

212 

100 

165 

73.8 

118 

47.7 

71 

21.6 

24 

— 4.4 

211 

99.4 

164 

73.3 

117 

47.2 

70 

21.1 

23 

— 5.0 

210 

98.8 

163 

72.7 

116 

46.6 

69 

20.5 

22 

— 5.5' 

209 

98.3 

162 

72.2 

115 

46.1 

68 

20.0 

21 

— 6.1 

208 

97.7 

161 

71.6 

114 

45.5 

67 

19.4 

20 

— 6.6 

207 

97.2 

160 

71.1 

113 

45.0 

66 

18.8 

19 

— 7.2 
























ELECTRICAL TABLES AND DATA 33 


Fah. 

Cent. 

Fah. 

Cent. 

Fah. 

206 

96.6 

159 

70.5 

112 

205 

96.1 

158 

70.0 

111 

204 

95.5 

157 

69.4 

110 

203 

95.0 

156 

68.8 

109 

202 

94.4 

155 

68.3 

108 

201 

93.8 

154 

67.7 

107 

200 

93.3 

153 

67.2 

106 

199 

92.7 

152 

66.6 

105 

198 

92.2 

151 

66.1 

104 

197 

91.6 

150 

65.5 

103 

196 

91.1 

149 

65.0 

102 

195 

90.5 

148 

64.4 

101 

194 

90.0 

147 

63.8 

100 

193 

89.4 

146 

63.3 

99 

192 

88.8 

145 

62.7 

98 

191 

88.3 

144 

62.2 

97 

190 

87.7 

143 

61.6 

96 

189 

87.2 

142 

61.1 

95 

188 

86.6 

141 

60.5 

94 

187 

86.1 

140 

60.0 

93 

186 

85.5 

139 

59.4 

92 

185 

85.0 

138 

58.8 

91 

184 

84.4 

137 

58.3 

90 

183 

83.8 

136 

57.7 

89 

182 

83.3 

135 

57.2 

88 

181 

82.7 

134 

56.6 

87 

180 

82.2 

133 

56.1 

86 

179 

81.6 

132 

55.5 

85 

178 

81.1 

131 

55.0 

84 

177 

80.5 

130 

54.4 

83 

176 

80.0 

129 

53.8 

82 

175 

79.4 

128 

53.3 

81 

174 

78.8 

127 

52.7 

80 

173 

78.3 

126 

52.2 

79 

172 

77.7 

125 

51.6 

78 

171 

77.2 

124 

51.1 

77 

170 

76.6 

123 

50.5 

76 

169 

76.1 

122 

50.0 

75 

168 

75.5 

121 

49.4 

74 

167 

75.0 

120 

48.8 

73 

166 

74.4 

119 

48.3 

72 


Cent. 

Fah. 

Cent. 

Fah. 

Cent. 

44.4 

65 

18.3 

18 

— 7.7 

43.8 

64 

17.7 

17 

— 8.3 

43.3 

63 

17.2 

16 

— 8.8 

42.7 

62 

16.6 

15 

— 9.5 

42.2 

61 

16.1 

14 

—10.0 

41.6 

60 

15.5 

13 

—10.5 

41.1 

59 

15.0 

12 

—11.1 

40.5 

58 

14.4 

11 

—11.6 

40.0 

57 

13.8 

10 

—12.2 

39.4 

56 

13.3 

9 

—12.7 

3S.8 

55 

12.7 

8 

—13.3 

38.3 

54 

12.2 

7 

—13.8 

37.7 

53 

11.6 

6 

—14.4 

37.2 

52 

11.1 

5 

—15.0 

36.6 

51 

10.5 

4 

—15.5 

36.1 

50 

10.0 

3 

—16.1 

35.5 

49 

9.4 

2 

—16.6 

35.0 

48 

8.8 

1 

—17.2 

34.4 

47 

8.3 

0 

—17.7 

33.8 

46 

7.7- 

- 1 

—18.3 

33.3 

45 

7.2- 

- 2 

—18.8 

32.7 

44 

6.6- 

- 3 

—19.4 

32.2 

43 

6.1- 

- 4 

—20.0 

31.6 

42 

5.5- 

- 5 

—20.5 

31.1 

41 

5.0- 

- 6 

—21.1 

30.5 

40 

4.4- 

- 7 

—21.6 

30.0 

39 

3.8- 

- 8 

—22.2 

29.4 

38 

3.3- 

- 9 

—22.7 

28.8 

37 

2.7- 

-10 

—23.3 

28.3 

36 

2.2- 

-11 

—23.8 

27.7 

35 

1.6- 

-12 

—24.4 

27.2 

34 

1.1- 

-13 

—25.0 

26.6 

33 

0.5- 

-14 

—25.5 

26.1 

32 

.0- 

-15 

—26.1 

25.5 

31 - 

-0.5 - 

-16 

—26.6 

25.0 

30 - 

-1.1- 

-17 

—27.2 

24.4 

29 - 

-1.6- 

-18 

—27.7 

23.8 

28 - 

-2.2 - 

-19 

—28.3 

23.3 

27 - 

-2.7- 

-20 

—28.8 

22.7 

26 - 

-3.3 



22.2 

25 - 

-3.8 




To convert degrees Centigrade into Fahrenheit, if 
the temperature given is above zero, multiply by 1.8 


34 


ELECTRICAL TABLES AND DATA 


and add 32. If it is below zero multiply also by 1.8, 
but if this product is less than 32, subtract it from 
32; if more, subtract 32 from it. To convert Fahren¬ 
heit into Centigrade, if the temperature given is above 
zero, subtract 32 and divide the remainder by 1.8; if 
below zero, add 32 and divide by 1.8. 

Concentric Wire. —Concentric wires are seldom 
used except in mines and similar places. Such a 
wire fully insulated would require more insulating 
material and be more bulky than the ordinary duplex 
wire. The concentric wire recently put upon the 
market has only one wire insulated. The other wire 
is a metal sheath which entirely surrounds the inner 
wire and its insulation. The sheath must always be 
thoroughly grounded. 

Condensers must be enclosed in noncombustible 
cases and installed with the same precautions as the 
wires of the system to which they attach. Con¬ 
densers are usually rated in microfarads, and a 
condenser of two or three microfarads is considered 
quite large. 

Conduits. —Conduit installations materially reduce 
the fire hazard, but to some extent increase the 
minor troubles. They produce many grounds and 
short circuits, but confine the trouble. Careful work¬ 
manship, especially at junction and outlet boxes, 
will reduce such troubles to a minimum. Install 
conduits so they will drain, and avoid their use in 
wet places unless lead-encased wires are used. 
Skilled conduit workers avoid the use of elbows with 
small wires as much as possible. The following 
tables (X and XI) give the sizes of conduits recom¬ 
mended by the National Electrical Contractors’ 
Association of the United States in connection with 
various sizes and numbers of wires. These recom¬ 
mendations are based on actual tests and can be 
relied upon. 


ELECTRICAL TABLES AND DATA 


35 


TABLE X 

Standard sizes of conduits for the installation of wires and 
cables as adopted and recommended by The National Elec¬ 
trical Contractors ’ Association of the United States and the 
N. E. Code. 

Conduit sizes are based on the use of not more than three 
90° elbows in runs taking up to and including No. 10 wires; 
and two elbows for wires larger than No. 10. Wires No. 8, 
and larger, are stranded. 

One Wire Two Wires Three Wires Four Wires 
Approx, in a Conduit in a Conduit in a Conduit in a Conduit 
B. & S. Diameter /—Diam.— , —Diam.—, , —Diam.—\ ,—Diam.— N 


Gauge 

of Wire Int. 

Ext. Int. 

Ext. 

. Int. 

Ext. 

Int. 

Ext. 

14 

18 /64 

v 2 

.84 

y 2 

.84 

V 2 

.84 

3 / 4 

1.05 

12 

2 %4 

y 2 

.84 

% 

1.05 

% 

1.05 

% 

1.05 

10 

2 %4 

y 2 

.84 

% 

1.05 

% 

1.05 

1 

1.31 

8 

2 %4 

y 2 

.84 

1 

1.31 

1 

1.31 

1 

1.31 

6 

i 

CO 

y 2 

.84 

1 

1.31 

iy 4 

1.66 

iy 4 

1.66 

5 

31 /64 

% 

1.05 

1 % 

1.66 

iy 4 

1.66 

iy 4 

1.66 

4 

3 %4 

% 

1.05 

iy 4 

1.66 

iy 4 

1.66 

iy 2 

1.90 

3 

3 %4 

% 

1.05 

iy 4 

1.66 

iy 4 

1.66 

iy 2 

L90 

2 

3 %4 

% 

1.05 

iy 4 

1.66 

iy 2 

1.90 

iy 2 

1.90 

1 

4 %4 

% 

1.05 

iy 2 

1.90 

iy 2 

1.90 

2 

2.37 

0 

4 %4 

i 

1.31 

iy 2 

1.90 

2 

2.37 

2 

2.37 

00 

4 %4 

i 

1.31 

2 

2.37 

2 

2.37 

2y 2 

2.87 

000 

5 %4 

i 

1.31 

2 

2.37 

2 

2.37 

2% 

2.87 

0000 

5 %4 

i y 4 

1.66 

2 

2.37 

2y 2 

2.87 

2y 2 

2.87 

250,000 

5 %4 

iy 4 

1.66 

2% 

2.87 

2% 

2.87 

3 

3.50 

300,000 

6 %4 

i y 4 

1.66 

2% 

2.87 

2y 2 

2.87 

3 

3.50 

400,000 

6 %4 


1.66 

3 

3.50 

3 

3.50 

3V 2 

4.00 

500,000 

7 %4 

i y 2 

1.90 

3 

3.50 

3 

3.50 

3y 2 

4.00 

600,000 

8 %4 

iy 2 

1.90 

3 

3.50 

3y 2 

4.00 



700,000 

8 %4 

2 

2.37 

3y 2 

4.00 

3y 2 

4.00 



800,000 

8 %4 

2 . 

2.37 

3 y 2 

4.00 

4 

4.50 



900,000 

9 %4 

2 

2.37 

3% 

4.00 

4 

4.50 



.1,000,000 

97 /64 

2 

2.37 

4 

4.50 

4 

5.00 



1,250,000 

1°% 4 

2% 

2.87 

4 ^ 

5.00 

4 % 

5.00 



1,500,000 

117 /64 

2y 2 

2.87 

4% 

5.00 

5 

5.56 



1,750,000 

12 %4 

3 

3.50 

5 

5.56 

5 

5.56 



2,000,000 

13 %4 

3 

3.50 

5 

5.56 

6 

6.62 






Duplex Wires 





14 

3 %4 

y 2 

.84 

% 

1.05 

1 

1.31 

1 

1.31 

12 

3 %4 

y 2 

.84 

% 

1.05 

1 

1.31 

1 V 4 

1.66 

10 

3 %4 

% 

1.05 

1 

1.31 

1% 

1.66 

iy 4 

1.66 


36 


ELECTRICAL TABLES AND DATA 


TABLE XI 

Standard sizes of conduits for the installation of wires and 
cables. 

3 Wire Convertible System 3 Wire Convertible System 


2 Wires 


Size 

2 Wires 


Size 

B.&S. 

1 Wire 

Conduit 

B. & S. 

1 Wire 

Conduit 

14 

10 

% 

00 

350,000 

2% 

12 

8 

% 

000 

400,000 

2y 2 

10 

6 

1 

0000 

550,000 

3 

8 

4 

1 

250,000 

600,000 

3 

6 

2 

m 

300,000 

800,000 

3 

5 

1 

i% 

400,000 

1,000,000 

3y 2 

4 

0 

i% 

500,000 

125,000 

4 

3 

00 

i % 

600,000 

1,500,000 

4 

2 

000 

i y 2 

700,000 

1,750,000 

4y 2 

1 

0000 

2 

800,000 

2,000,000 

4y 2 

0 

250,000 

2 




Single Wire Combination. 

Number of single No. 14 wires in one conduit. Straight run; 
no elbows. Special permission is required. 

Conduit Size 


3 No. 14 rubber covered double braid. % 

5 No. 14 rubber covered double braid. % 

10 No. 14 rubber covered double braid. 1 

18 No. 14 rubber covered double braid. 1 % 

24 No. 14 rubber covered double braid. 1% 

40 No. 14 rubber covered double braid. 2 

74 No. 14 rubber covered double braid. 2% 

90 No. 14 rubber covered double braid. 3 


Signal Systems. 
Straight runs; no elbows. 


No. Wires B.& S. Conduit Sizes 

10 16 Lt. ins. fixture wire. % 

20 16 Lt. ins. fixture wire. % 

30 16 Lt. ins. fixture wire. 1 

70 16 Lt. ins. fixture wire. 1*4 

90 16 Lt. ins. fixture wire. 1% 















ELECTRICAL TABLES AND DATA 


37 


No. Wires B.& S. Conduit Sizes 

150 16 Lt. ins. fixture wire. 2 

18 18 Lt. ins. fixture wire^. y 2 

30 18 Lt. ins. fixture wire. % 

40 18 Lt. ins. fixture wire. 1 

100 18 Lt. ins. fixtrue wire. 1^4 

130 18 Lt. ins. fixture wire. 1 y 2 

200 18 Lt. ins. fixture wire. 2 


Telephone Circuits. Not more than two 90° Elbows. 


No. 19 braided 

and twisted 

No. 20 braided 

and twisted 

pair switchboard or desk 

pair switchboard or desk 

instrument 

wires. 

instrument 

wires. 

No. Pairs 

Conduit 

No. Pairs. 

Conduit 

3 . 

. y 2 

5 . 

. 34 

6 . 

. % 

10 . 

. % 

10 . 

. 1 

15 .. 

. 1 

16 . 

. 114 

25 .. 

. 134 

25 . 

. 134 

35 .. 

. iy 2 

35 . 

. 2 

50 . 

. 2 


Conduits and Wires.—Two sides of the smallest 
rectangular enclosures that will contain a given 

D 

number of wires are : (D x a) + — and Dxbx86. D 

2 


being the diameter of the wire, a the number of wires 
in longest row, and b the number of rows. 

The nearer square this enclosure can be made, the 
greater the economy of material. The greatest number 
of wires that can be placed in a rectangular enclosure 




H 


D x .86, 


L being the length of the enclosure, H the height, 
and D the diameter of the wire. 

This formula is only approximate and in using it 

T J£ 

all fractions obtained by and ^must be 

D Dx.8Q 


dropped. 
























38 


ELECTRICAL TABLES AND DATA 


Example.—Given an enclosure 6 inches long and 2 
inches high, how many wires can it hold, the diam¬ 
eter of each wire being .7 ? 6 divided by .7 equals 

8.6. Dropping the .6 and subtracting we have 7.5 
for the first factor. Next, .7 times .86 equals .602; 
2 divided by this equals 3.3; dropping the .3, we 
now have to multiply the 7.5 by 3, which equals 22.5, 
or 22 wires. 

For circular enclosures no general formula can 
be given because the percentage of waste space 
varies greatly with different wires. The first chart 
may be used to determine the smallest conduit that 
will enclose a certain number of wires. This chart 
shows graphically how nearly different numbers of 
wires fill out circular spaces. To use this chart, 
multiply diameter of wire by the number given in 
connection with circle containing the requisite num¬ 
ber of wires. This will give the smallest diameter 
of tube or conduit that will receive these wires. 
How much larger the conduit to be used must be 
depends upon circumstances. The number and na¬ 
ture of bends, nature of insulation, flexibility of 
wire, as well as temperature and inspection require¬ 
ments, must be taken into consideration. 

The charts illustrate the relative spaces occupied 
by the different conduits, viz.: 3", 2-|", 2", 1J", 1£", 
1", etc., and the ydres considered. The sizes of con¬ 
duits are marked in the various circles and each 
horizontal row pertains to one size of wire, with 
exception of the 4th and 5th in each row and a few 
at the top of one of the charts. The 4th shows a 
neutral wire of half the carrying capacity, and the 
5th of double the carrying capacity of the outside 
wires. The different sizes of conduit given in each 
case will enable one to judge the most appropriate 
size to be used under different circumstances. The 
wires shown are all double braid stranded cables. 



40 


ELECTRICAL TABLES AND DATA 


1000000 

C.M. 



800000 C. M. 


1250000 

C.M. 





1500000 

C. M. 



900000 C. M. 




600000 C. 




700000 C. 






500000 C.M 



400000 C.M. 





300000 C. M. 



250000 C. M. 























ELECTRICAL TABLES AND DATA 


41 


















42 


ELECTRICAL TABLES AND DATA 


In the preceding pages are given the conduit sizes 
recommended.by the National Electrical Contractors 7 
Association of the United States. These should be 
followed as far as they apply. 

Contacts.—The standard materials for mounting 
contacts are slate, marble, porcelain, and glass. 
Where these are liable to breakage, other materials 
are allowed, but they should always be submitted 
to inspection departments for approval. A surface 
contact of one square inch for each 75 amperes is 
good practice for knife-switches and similar devices. 

Controllers. —Methods of motor and light control 
are numerous. Lights are usually controlled by 
cutting resistance into the mains. A certain con¬ 
troller is suitable only for a certain number of lights 
requiring a certain amperage. The reduction of 
voltage is equal to the product of the amperes times 
the resistance, and the effect upon the lights is 
greater than indicated by the drop in voltage. The 
speed of motors may be altered by cutting resist¬ 
ance into the mains, altering the field connections, 
arranging taps of different voltages, and connecting 
armatures in multiple or series. 

Cooking. —Almost any kind of cooking can be 
accomplished electrically, but the expense is higher 
than with gas. It is best to be honest and advise 
customers correctly about these things than to 
cause disappointment. The advantages are con¬ 
venience and rapidity of results with many of the 
devices. 

Cooper-Hewitt Lamps (Mercury Vapor).—These 
lamps may be obtained for either alternating or 
direct-current use, and for 110 or 220 volts. The 
light given out is of a greenish hue, and gives a 
ghastly effect to faces and hands. Many persons 
object to working under it, while others seem to 
like it. The efficiency of the lamp compares favor- 


ELECTRICAL TABLES AND DATA 


43 


ably with others; it is easy to operate, and the light 
is practically shadowless. With alternating currents 
the light flickers somewhat, and is said to give a 
deceptive appearance to some surfaces. Not more 
than one lamp should be installed on one circuit. 
Use double-pole switches and avoid plug cut-outs for 
220 volts. Current sent through direct-current lamps 
in wrong direction will ruin tubes. Where inflam¬ 
mable gases exist, the sparking of some of the lamps 
is dangerous. The life of a tube is now claimed to 
be 5000 hours. The current ranges from 3.5 to 2.0 
amperes for different types, and the efficiency is 
given as from 0.51 to 0.64 watts per mean lower 
hemispherical candle power. The light is mostly 
thrown downward. 

Copper weighs about 556 pounds per cubic foot; 
its specific gravity is about 8.9, and it melts at 1196 
degrees Fahrenheit. The tensile strength of an¬ 
nealed copper may be taken as about 35,000 pounds 
per square inch, and that of hard drawn copper as 
about 55,000. 

Cross Currents pass between A.C. generators, and 
also between synchronous motors when they are 
operating in parallel and not perfectly in phase. 
These currents heat the wires and overload the 
machines unnecessarily. 

Cut-outs. —In connection with installations served 
by central stations, the type of cut-out and fuse 
preferred by that company should be installed. This 
will usually obtain free fuse renewals. The installa¬ 
tion of cartridge-type fuses is not advisable except 
in establishments where a competent electrician is 
always on duty. 

The dimensions of several types of cut-outs are 
given below. 


44 


ELECTRICAL TABLES AND DATA 


TABLE XII 

Paiste Panel Cut-Outs (See Figure 2). 

125 Volt Sizes. Capacity of Switches 30 Amperes 



No. 

4103 


No. 

4101 


No. 

4105 


Cat. No. 

Main 

Branches 

Width 

(inches) 

Length 

(inches) 

4012 

2-Wire 

Single, 2-Wire 

3% 

5% 

4015 

2-Wire 

Double, 2-Wire 

3 

ioy 8 

4026 

3-Wire 

Single, 2-Wire 

3% 

7% 

4013 

3-Wire 

Double, 2-Wire 
Single, 3-Wire 

3y« 

10% 

4103 

3-Wire 

5 

8% 

250 

Volt Sizes. 

Capacity of 

Switches 30 

Amperes 

=4101 

2-Wire 

Single, 2-Wire 
Double, 2-Wire 

3% 

7 

=4105 

2-Wire 

3% 

11% 


























































































ELECTRICAL TABLES AND DATA 


45 


TABLE XIII 


Dimensions for Plug Cut-Outs (See Figure 3). 



No. 25 69 



No. 2^65 





No. 8020 




No. 





Figure 3.—Plug Cutouts. 


Cat. No. 


2569 

2965 

2165 

8020 

1935 

2587 

2150 

2199 

8042 

2135 


Length 

(inches) 

2 % 

2V 2 

2 j % 

3% 

m 

4% 

6tk 

4M 

ey 8 


Width 

(inches) 

2 

3^5 

4y 2 

3% 

3t*s 

3 

3 

2i§ 

4JI 

4* 


Height 

(inches) 

Hi 

HI 

HI 

iy 2 

HI 

Hi 

HI 

HI 

HI 

Hi 



































































































46 


ELECTRICAL TABLES AND DATA 



Fig 6 TP O B ^ Fig 12 2W|^CrotaOw 


Figure 4.—D. & W. Cutouts. 


































































































































































































































































































































































ELECTRICAL TABLES AND DATA 


47 


TABLE XIY 


Dimensions of D. & W. 250 Volt Cut-Outs (See Figure 4). 


Amperes 

Fig. 

A 

B 

C 

D 

E 

0-30 

1 

3f 

1 

Its 

3f 

n 

0-30 

2 

3i^ 

2f 

1‘15 

3fk 

n 

0-30 

3 

3fk 

4 

ll 9 5 

3^ 

1 * 

0-30 

4 

4* 

2f 

1* 

4* 

H 

0-30 

5 

6 

4 

1& 

6 

1 * 

0-30 

10 

74 

2i 

1i 9 s 

7* 

11 

0-30 

6 

811 

4* 

li 9 s 

811 

11 

0-30 

11 

811 

2* 

ll 9 5 

8 If 

11 

0-30 

12 

H 

3f 

1 T5 

3f 

11 

31-60 

1 

4* 

If 

1** 

6* 

2f 

31-60 

2 

4f 

3i 7 s 

If 


1t 9 5 

31-60 

3 

4i 

O 

If 

5* 

ll 9 5 

31-60 

4 

61 

3i 7 s 

If 

61* 

1* 

31-60 

5 

8 

5 

If 

83 ^ 

l^S 

31-60 

10 

10** 

3f 

21 

Hf 

Hf 

31-60 

6 

12 


21 

12* 

Ilf 

31-60 

11 

12 

31f 

2i 

12* 

iff 

61-100 

7 

61 

2* 

2ts 

64 

4f 

*61-100 

8 

8* 

4i 3 s 

2i 5 s 

8* 

1*4 

61-100 

9 

8* 

6* 

2& 

8f 

ill 

101-200 

7 

n 

2* 

3f 

8* 

54 

201-400 

7 

n 

3f 

4* 

101 

64 

401-600 

7 

ii 

31 

4f 

12* 

8* 


Delta Connection,—This method of connection is 
used only with three-phase a. c. currents. If the 
connection of a generator is changed from “star” 
to “delta,” its current will be increased 1.73 times 


48 


ELECTRICAL. TABLES AND DATA 


for the same power delivery. If it is changed from 
“delta” to “star,” its e.m.f. will be increased 1.73 
times. A synonymous term for delta is “mesh.” 

Demand Factor. —At present it is customary among 
inspection bureaus to demand conductor capacity 
equivalent to the whole connected load operating at 
its maximum capacity. Experience, however, has 
shown that in many cases this leads to a great waste 
of copper. 

In very many installations it has been found that 
not over 20 per cent of the connected load is ever in 


, ft 


Jr 





B 











a 









- 

rs 









■>. 

S, 

s. 




















Demand Factor Chart. 


use at the same time. Tables of demand factors ap¬ 
plicable to many classes of service have been worked 
out and are in existence. But as far as the authors are 
aware, these are all arranged from the standpoint of 
the central station engineer and are hardly applicable 
to individual installations. As a matter of fact, the 
authors have failed to find any two installations, eveu 
in the same line of business, quite alike. 






























ELECTRICAL TABLE'S AND DATA 


49 


INDIVIDUAL MOTORS 

Many motors are now designed and rated to carry 
a certain overload, usually 25 per cent, for a short 
time. This fact should be taken into account wher¬ 
ever it seems necessary. Whenever motors are de¬ 
signed for a short time rating, instead of for con¬ 
tinuous use, it seems but right that the conductors be 
chosen with the same length of time in view. Insofar 
as the heating of conductors is concerned, it is un¬ 
necessary to pay any attention to the ordinary start¬ 
ing current. The only justification for the ex¬ 
cessive carrying capacity usually demanded for in- 
* dividual motors, lies in a possible necessity to take 
care of overloads. 

GROUPS OF REGULARLY REVERSING MOTORS 

A graphic representation of current values in a 
series of cycles of operation of a reversible motor 
operating a large washing machine is given in Figure 
4b. In connection with such motors, it is quite usual 
to reverse without giving the armature time to come to 
rest. The reversed current through the armature 
must first bring the machinery to rest and then start 
it in the opposite direction. The majority of such 
motors reverse at intervals of 10 or 12 seconds and 
the average peak current lasts about one second. 

In this connection it will be well to note that, in 
order to give this study a practical value, we must 
take a course about midway between absolute accu¬ 
racy and haphazard guess work. The heating effect 
of various kinds of motor loads cannot be accurately 
determined without the use of graphic current charts 


50 


ELECTRICAL TABLES AND DATA 


and these are seldom available at the time the installa¬ 
tion is made. The contractor and the inspector are 
thus, in the majority of cases, compelled to judge by 
the rated h. p. of the motors required. In order, 
therefore, to make these tables of general use to the 
public, the carrying capacity of conductors required 



Figure 4b 

must be based upon the h. p. intended to be installed. 
It is principally for this reason that the following 
table has been arranged in the form given. 

The table gives factors which express the ratio of 
the h. p. equivalent of intermittent or fluctuating 
currents to the heating equivalent of the same cur¬ 
rents. The h. p. value of a fluctuating current (volt¬ 
age assumed constant) is proportional to the average 
sum of all the ordinates of a curve representing it. 
The heating effect of the same current is proportional 
to the r. m. s. value of the same ordinates. Thus, if 
we divide the r. m. s. value of a certain fluctuating 
current by its h. p. value, we shall obtain a factor by 
which we may multiply the h. p. delivered by a motor 
in such service in order to find the amperage for which 
conductor capacity should be provided to guard 
against overheating. 






















ELECTRICAL TABLES AND DATA 50a 

At the top of the table we have the various per¬ 
centages of time of minimum and peak currents. In 
the first vertical row we have various percentages of 
peak currents expressed in terms of the minimum 
current used. In this form we may use the factors in 
connection with the rated h. p. of the motors, pro¬ 
vided we know, in a general way, the approximate 
ratio of the minimum to the peak currents required 
by the fluctuating load. 

As an example: If we have a motor reversing 
regularly and requiring a peak current five times as 
great as its running current, and this during half of 
the time of each cycle, we look where the lines per¬ 
taining to 50 per cent peak and minimum current 
time cross the line pertaining to the 500 per cent 
peak, and find there the factor 1.21, which indicates 
that the amperage to be provided for must be 1.21 
times that called for by the h. p. rating of the motor. 


Table 


Percent time 


of peak current. 10 
Percent time 

20 

30 

40 

50 

60 

70 

min. current... 

. 90 

80 

70 

60 

50 

40 

30 

Percent 

r 200% 

1.04 

1.05 

1.06 

1.06 

1.05 

1.04 

1.04 

peak load 

300% 

1.12 

1.15 

1.15 

1.14 

1.12 

1.10 

1.07 

in terms 

400% 

1.22 

1.25 

1.23 

1.21 

1.17 

1.13 

1.10 

of min. 

500% 

1.31 

1.34 

1.30 

1.26 

1.21 

1.16 

1.11 

load. .< 

600% 

1.41 

1.42 

1.37 

1.29 

1.23 

1.18 

1.12 


700% 

1.50 

1.50 

1.40 

1.32 

1.25 

1.19 

1.13 


800% 

1.59 

1.54 

1.44 

1.35 

1.27 

1.20 

1.15 


900% 

1.67 

1.59 

1.47 

1.37 

1.28 

1.21 

1.15 


. 1000% 

1.74 

1.63 

1.50 

1.39 

1.29 

1.22 

1.15 


80 90 

20 10 
1.04 1.01 
1.05 1.02 
1.07 1.03 
1.07 1.03 
1.08 1.04 
1.09 1.04 
1.09 1.04 
1.09 1.04 
1.09 1.04 


The factors here given are correct for single motors 
and are based on the worst possible condition under 
which a group of motors can operate; viz., all peaks 
superimposed. This is a condition which may at times 



50b 


ELECTRICAL. TABLES AND DATA 


be attained, but if a large group of motors is con¬ 
sidered, the chance of its recurrence is exceedingly 
small. 

With these considerations in view, we deduce the 
following formula to find the fraction of the total 
time during which the peaks of all the motors in use 
are likely to be superimposed: 

A h 

In this formula, A represents the fraction of the 
time of a cycle of operation during which the peak 
is in use, and b the number of motors in use. In the 
case of laundry motors of the characteristics shown 
in Figure 4b, the peaks, when once coincident, will 
remain so for some length of time or until one or more 
have been stopped and the combination broken. In 
the case of elevator motors the combination will al¬ 
most immediately be broken. 

GROUPS OF REVERSING MOTORS WITH VARIABLE TIME 

INTERVALS 

In many machine shops the planers are equipped 
with reversing motors. Some very clever systems of 
<*)ntrol have been worked out and in some of these 
the carriage is made to return at a high rate of speed 
after making the cut. The length of time during 
which such a motor moves in either direction is 
variable and the power required by the forward and 
return strokes is also variable. The periodicity, as 
well as the relative amount of current, vary and are 
governed by the work in hand. 

Since there is no permanent regularity about any 

of the operations, no exact forecast as to what will 

happen at any particular time can be made. A studv 

«/ 


ELECTRICAL TABLES AISID DATA 


50c 


of the conditions as illustrated in Figure 4e will, 
however, assist materially in judging what the cur¬ 
rent demands of a group of such motors may be at 
times. 

In the figure we have five motors, denoted by black 
circles, in operation and reversing regularly at in¬ 
tervals of 12, 6, 8, 4 and 9 seconds. An inspection of 
the figure will show at a glance that, with any num- 



Figure isc 

ber of motors, if they start in synchronism, the time 
of coincidence of the peak of all of them will be pro¬ 
portional to the least common multiple of all of their 
time intervals. In this case that number is 72; hence, 
at intervals of 72 seconds these motors will all come 
into synchronism as far as their peaks are concerned. 
Their minima of current will, of course, also come into 
synchronism regularly. 

If they do not start in synchronism, those starting 
at time intervals which form a multiple of their own 
time, remote from that of other motors, will work into 
synchronism and out of it in a perfectly regular 
manner, just as will those shown in the figure. Those 
that start at different time intervals, however, will 
not. 

As an example, if the motor having a period of 6 
seconds starts either 1, 2, 3, 4, 5, 7, 8, 9, 10 or 11 
seconds after the other, it will never superimpose its 















































































50d 


ELECTRICAL TABLES AND DATA 


peak entirely upon that of the other, although a part 
of it may overlap. It must, however, be borne in mind 
that the motor having the shortest periods governs 
the chances of falling into step. A motor having a 
period of 4, for instance, will have only one chance 
in 4 of missing regular synchronism of peaks with 
other motors having periods of 8 or 12. With motors 
on this kind of work then, we may be certain that 
there will be coincidence of peaks at times. In con¬ 
nection with motors of this kind it will be safe to use 
about the average multipliers given in the table, the 
average being determined from the characteristics of 
the different motors. 

PASSENGER ELEVATOR AND SIMILAR MOTORS 

In the kind of service here considered, the current 
is either entirely on or off. If calculations are to be 
based upon current or power charts the equivalent 
current of a cycle of operations should be determined 
by the r. m. s. method. The formulae and the tables 
herewith furnished, however, are so arranged that, 
for general purposes, we need merely know the rated 
h. p. of the whole group and the relative time of the 
on and off periods. 

In the preliminary operation of finding the current 
required it is to be assumed that the motors are de¬ 
livering their rated capacity continuously, regardless 
of the nature of their rating. The formula given 
below is also independent of the number of motors 
and the demand factor obtained is a function of the 
relative on and off times of the motors, which is 
assumed to be the same for all. 

A conductor is used to the best advantage with 


ELECTRICAL TABLE'S AND DATA 


50e 


reference to heating when subjected to a steady cur¬ 
rent flow. Hence, if another conductor be called upon 
to transmit an equivalent amount of energy with 
intermittent service, the carrying capacity of the 
second conductor must be correspondingly increased. 
If the load is of such a nature that the conductor is 
idle half of the time, it must carry double current 
during the other half of the time. As the heating is 
proportional to the square of the current, it follows 
that a double current during half time is equivalent 
in heating effect to \/2 times the normal current used 
continuously. The same relation holds for all other 
time divisions and this will allow us to find the value 
of a steady current, to be denoted by /, which will 
be the equivalent of any regularly intermittent cur¬ 
rent of the nature here considered by the formula as 
given below: 



where i is the theoretical current based on the total 
motor rating, t the fraction or percentage of time in 
a cycle of operation during which the motor is using 
this current, and V the time of a complete cycle of 
operation. This formula will give us a multiplier, 
virtually a demand factor, by which we can find the 
current having an equivalent heating effect to that 
required by the motors under the assumption that 
they are all working under the worst possible condi¬ 
tion, i. e., all motors taking their maximum current 
at the same instant. 

The factors calculated according to the formula 
as applying to the various percentages of time dur- 




50f 


ELECTRICAL TABLES AND DATA 


ing which the current is in use, are given below. The 
upper line gives the percentage of time during which 
current is used, and the lower line gives the multiply¬ 
ing factors. 

Percentage of Time. 10 20 30 40 50 60 70 80 90 

Factors .32 .45 .55 .66 .71 .78 .84 .89 .95 

GROUPS OP MOTORS OF INDISCRIMINATE CHARACTERISTICS 

This classification embraces all kinds of motors as 
usually found in shops and factories. There are two 
ways of arriving at the probable demand factor of 
such groups. One way consists of consulting tables 
made up from experiences with similar installations. 
This method has the great disadvantage that it is 
almost impossible to find two installations near enough 
alike to warrant very accurate comparisons. Such 
tables are given further on, but should be used only 
as general guides and the final determination made 
only after making a careful analysis of the installa¬ 
tion. 

A simple method of analyzing a motor installation 
and determining its demand factor is as follows: Take 
any piece of ordinary ruled paper and number as 
many lines as there are hours of the day to be con¬ 
sidered. Let these lines be horizontal. Next draw as 
many lines vertically across them as there are motors 
to be considered. Also place each line so that in 
position and length it may cover the hours of the day 
during which the motors are thought to be in use. 

There are two ways in which such a representation 
can be made. If the motors have no fixed time at 
which they run, their running time may be laid out 
at the bottom of the figure; the main point being that 



ELECTRICAL TABLE'S AND DATA 51 

the lines give a fair idea of the proportionate running 
time per day. If the stopping and starting intervals 
are not too short, a series of such lines, representing 
the estimated number of starts, may be used. 

If any of the motors are used only during certain 
hours of the day, the line pertaining to these motors 
may be placed in the horizontal lines pertaining to the 
hours of the day, as for instance A and B in the figure. 
These two motors never interfere with each other, but 
do occasionally come in at the same time with some of 
the other motors plotted at the bottom of the line. 

Department Stores. —Such places usually require 
large quantities of powder for illumination, electric 
signs, and motors. The demand factor for lighting 
is very close to 100 per cent. If economy is not 
too much insisted upon, a bountiful circuit capacity 
should be provided. This will allow brilliant illumi¬ 
nation wherever it is needed. As department stores 
contain nearly all of the goods handled in other 
stores, hints on illumination of special places should 
be looked up under the corresponding headings— 
dry goods stores, jewelry, etc. As there are usually 
large areas visible from any one place, good appear¬ 
ance demands some uniform arrangement of fixtures. 
If this does not provide sufficient light for certain 
goods in show cases, local illumination is provided 
in the cases. If branch circuit capacity for five 
watts per square foot is provided, it will enable 
very brilliant illumination of spots wdthout over¬ 
loading circuits and not interfere with the frequent 
changes which are made. The capacity of general 
mains need not be greater than two watts per square 
foot on the most important flows. 


52 


ELECTRICAL TABLES AND DATA 


Depreciation.—Depreciation must be duly consid¬ 
ered in dealing with any form of apparatus. The 
depreciation is governed entirely by the useful life 
of the device, but this in turn is governed by the 
amount of wear and tear which cannot be repaired 
for from time to time; obsolescence, possibly in¬ 
adequacy after a time, or probable cessation of busi¬ 
ness. Depreciation should not be confused with 
maintenance, to which should be charged all mis¬ 
haps which do not permanently lessen the natural 
useful life of the apparatus. From 10 to 20 per cent 
is often charged to depreciation, but it is better to 
estimate it carefully in each case unless a parallel 
case is well understood. 

Desk Lighting.—The illumination of desks by indi¬ 
vidual lamps is never to be advised, except in the 
case of individuals with very poor eyesight or in 
locations where desks are far apart or used but a 
few hours per day. Where individual desk lighting 
is provided, the cost of energy may sometimes be 
lower, but the first cost of installation, and also 
maintenance, is always high. There is, further, al¬ 
ways a considerable fire hazard, and all of these 
offset the saving in energy to a large extent. A 
general and fairly shadowless illumination also adds 
much to the efficiency of clerks. The following 
table shows the comparative cost of proper general 
illumination as compared with local for desks of 
various spacing. It is assumed that a general illumi¬ 
nation of 1J watts per square foot is provided, and 
that at each desk a 25-watt lamp is also used, wdiile 
the general illumination with which this desk light¬ 
ing is compared is obtained through the medium of 
the most efficient large wattage lamps at present on 
the market. One watt per square foot will give 
good general illumination, which will need to be 
helped out by local lighting only for persons with 


ELECTRICAL TABLES AND DATA 


53 


weak eyes. Where local desk lighting is resorted 
to the wattage requirements will be about as 
follows: 


Av. sq. ft. per desk... .20 25 30 35 40 45 50 

Total watts per sq. ft.. 1.5 1.25 1.08 0.96 0.87 0.80 0.75 

It will be noted that where desks are close to¬ 
gether the general illumination is not only the easiest 
installed but also the cheapest to operate. If the 
desks are used only a small part of the time the 
local illumination will be the cheaper. Lamps used 
for desk lighting should either be frosted or encased 
in diffusing globes. 

Diamagnetic.—Zinc, antimony, bismuth, and cer¬ 
tain other metals are repelled when placed between 
the poles of strong magnets, and are said to be dia¬ 
magnetic. Metals which are attracted by magnetism 
are said to be paramagnetic. 

Dielectric.—Any substance which is an insulator 
and allows electrostatic induction to take place 
through its mass. Usually taken as synonymous 
with insulation. 

Dry Kilns.—Such places are too hot for rubber- 
covered wire. Use asbestos-covered. Place cut-outs 
and switches outside. 

Eddy Currents.—Useless currents which are pro¬ 
duced in the iron of pole pieces, etc., subject to 
motion in a magnetic field, or to the influence of 
coils in which a fluctuating current exists. They 
cause a waste of energy and heat the metal. 

Efficiency.—The efficiency of motors, transformers, 
and other similar translating devices is found by 
dividing the output by the input. In connection 
with sources of electric illumination the term 
efficiency has an entirely different meaning. The 
efficiency of such devices is spoken of as a certain 


64 ELECTRICAL TABLES AND DATA 

number of watts per candle power. In this case, 
the higher the efficiency, the more uneconomical is 
the lamp. See Motors and Illumination for practical 
applications. 

Egg Candling.—One light must be provided for 
each workman, and it should be located about waist 
high. The wires should be run at this height so 
as to avoid use of long cords. The light is always 
made adjustable, and is encased in a small metallic 
hood with a small opening. 

Electric Braking.—This is also sometimes termed 
* ‘dynamic braking/’ If an electric motor is dis¬ 
connected from its source of supply, and its arma¬ 
ture circuit closed while the armature is still in 
motion, it will generate current and consume power, 
and may be brought to rest very quickly in this 
manner. Where the necessary provisions for this 
purpose are installed this method of braking is very 
successful. 

Electrolysis.—Nearly all electrolysis is due to the 
fact that piping and other metallic structures near 
a ground return system of electrical distribution 
afford a return circuit of such low resistance as 
compared to the return circuit provided, that a 
large part of the current returns over the piping. 
It is impossible to prevent electrolysis entirely ex¬ 
cept by insulating the return wires. The troubles 
may, however, be materially reduced. The current 
does damage only where it leaves the pipes or other 
structures which it has entered, and the damage is 
in proportion to the amperes carried. The methods 
used for lessening electrolysis are the following: 

1. Protection of structures by concrete or other 
forms of insulation, or keeping them as far as pos¬ 
sible from ground return circuits. Insulation of 
piping is not advisable; it is likely to concentrate 
the trouble at spots where it is poor. 


ELECTRICAL TABLES AND DATA 


55 


2. Bonding pipes, etc., so as to prevent current 
which, has once entered them from leaving, except 
at predetermined places, and then never to earth. 

3. Negative boosters have been suggested, but 
have not been extensively tried. A negative booster 
is a low-voltage dynamo connected into the return 
circuit in such a manner as to draw current from 
the rails and earth and deliver it back to the sta¬ 
tion. 

4. Reinforcing the rails, etc., by large conductors, 
thus increasing the conductivity of the return, and 
lowering the p. d. between the rails and the sta¬ 
tion. 

In most cities ordinances mention the difference 
in potential which may be allowed to exist between 
any two points on the return wires. In Chicago it 
is provided that all uninsulated electrical return 
circuits must be of such current-carrying capacity 
and so arranged that the difference of potential 
between any two points on the return circuit will 
not exceed the limit of twelve volts, and between 
any two points on the return 1000 feet apart within 
a one-mile radius of the City Hall will not exceed 
the maximum limit of 1 volt, and between any two 
points on the return 700 feet apart outside of this 
one-mile radius limit will not exceed the limit of 1 
volt. In addition thereto, a proper return conductor 
system must be so installed and maintained as to 
protect all metallic work from electrolysis damage. 
The return current amperage on pipes and cable 
sheaths must not be greater than 0.5 amperes per 
pound-foot for caulked cast iron pipe, 8.0 amperes 
per pound-foot for screwed wrought iron pipe, and 
16.0 amperes per pound-foot for standard lead or 
lead alloy sheaths of cables. 

All insulated return current systems must be 
equipped with insulated pilot wire circuits and volt* 


56 


ELECTRICAL TABLES AND DATA 


meters, so that accurate chart records will be obtain¬ 
able daily, showing the difference of potential be¬ 
tween the negative bus-bars in each station and at 
least four extreme limits on the return circuit in its 
corresponding feeding district. Also with recording 
ammeters, insulated cables, and automatic reverse 
load and overload circuit breakers which will record 
and limit the maximum amperes drained from all 
the metallic work (except the regular return feed¬ 
ers) to less than 10 per cent of the total output of 
the station. Figuring on the basis of the average 
resistance of cast iron, wrought iron, and lead, the 
above amperages will exist with the following differ¬ 
ence of potential per running foot, and will be inde¬ 
pendent of the thickness or size of pipe: Cast iron, 
0.000711 volt per foot; measurements must be taken 
on solid pipe and not across any joint. Wrought 
iron, 0.001568 volt per foot; measurement to be 
taken as above. Lead sheaths, 0.007497 volt per 
foot; as joints in lead sheaths are always soldered 
and wiped, no attention need be paid to them. The 
lower amperage for the iron piping is specified be¬ 
cause joints will usually be found of higher resist¬ 
ance than the piping, and at each joint current is 
likely to leave piping and enter it again just 
beyond. 

The proper treatment of electrolysis may require 
all four methods outlined above. The method most 
to be recommended in a general way is that of re¬ 
inforcing the return conductors sufficiently to limit 
the difference of potential as prescribed. 

The following table shows the size of copper con¬ 
ductors necessary with rails of various weights per 
yard to reduce electrolysis to -J, J, and J, etc.; the 
specific resistance of the rails being taken as 10 
times that of copper, and the resistance of bonds as 
negligible. 


ELECTRICAL TABLES AND DATA 


57 


TABLE XV 


of electrolysis to 
given. 

Weight of Circular 

the fraction 

of its original value 

Rails Per 
Yard 

Mils 
of Rail 

1-2 

1-3 

1-4 

40 

4 , 950,000 

495,000 

990,000 

1 , 485,000 

45 

5 , 600,000 

560,000 

1 , 120,000 

1 , 680,000 

50 

6 , 230,000 

623,000 

1 , 246,000 

1 , 869,000 

60 

7 , 500,000 

750,000 

1 , 500,000 

2 , 250,000 

70 

8 , 770,000 

877,000 

1 , 754,000 

2 , 631,000 

80 

9 , 900,000 

990,000 

1 , 980,000 

2 , 970,000 

90 

11 , 200,000 

1 , 120,000 

2 , 240,000 

3 , 360,000 

3 , 750,000 

100 

Weight 

12 , 500,000 

Circular 

1 , 250,000 

2 , 500,000 

of Rails 

Per Yard 

Mils 

of Rail 

1-5 1- 

6 1-7 

1-8 


40 4 , 950,000 1 , 980,000 2 , 475,000 2 , 970,000 3 , 465,000 

45 5 , 600,000 2 , 240,000 2 , 800,000 3 , 360,000 3 , 920,000 

50 6 , 230,000 2 , 492,000 3 , 115,000 3 , 738,000 4 , 361,000 

60 7 , 500,000 3 , 000,000 3 , 750,000 4 , 500,000 5 , 250,000 

70 8 , 770,000 3 , 508,000 4 , 385,000 5 , 262,000 6 , 039,000 

80 9 , 900,000 3 , 960,000 4 , 950,000 5 , 940,000 6 , 930,000 

90 11 , 200,000 4 , 480,000 5 , 600,000 6 , 720,000 7 , 840,000 

100 12 , 500,000 5 , 000,000 6 , 250,000 7 , 500,000 8 , 750,000 


For a comprehensive treatment of electrolysis a map 
of the return circuits and adjacent piping should be 
made. Tests determining p. d. and direction of cur¬ 
rent should be made, and results marked upon the 
map. In many cases currents will be found in oppo¬ 
site direction at the same point at different times. 
In estimating the current strength from p. d. noted 
between track and piping the distance of the latter 
from the track must be taken into consideration. 
If this is small a low p. d. may deliver considerable 
current. Often the trouble can be reduced suffi¬ 
ciently by running comparatively short lengths of 
heavy copper. In testing p. d.’s it is best to use a 
sensitive galvanometer. Such an instrument may 
be calibrated with reference to a milli-volt meter. 


58 


ELECTRICAL TABLES AND DATA 


TABLE XVI 

The table below shows the approximate amperage 
per milli-volt p. d. per foot which will be found in 
the various kinds and sizes of piping and sheaths 
given. 

Cast Iron, Average Wrought Iron, Average Lead Sheaths, 


Inside 

wt., 

Am¬ 

Inside 

wt.. 

Am¬ 

Outside 

Amperes 

Diam. 

Per Ft. 

peres 

Diam. 

Per Ft. 

peres 

Diam. 

Approx. 

3 

16 

12 

* 

.87 

4$ 

1.26 

5 

4 

22 

15 

t 

1.15 

5* 

1.50 

6 

6 

35 

25 

1 

1.70 

8 

1.58 

6 

8 

50 

37 

u 

2.25 

11 

1.65 

6.6 

10 

67 

50 

1* 

2.75 

14 

1.68 

6.9 

12 

87 

65 

2 

3.60 

18 

1.72 

7.0 

14 

110 

82 

2} 

5.80 

30 

1.78 

7.1 

16 

135 

102 

3 

7.65 

40 

1.84 

7.2 

18 

165 

123 

3* 

9.00 

48 

1.90 

7.5 

20 

190 

141 

4 

11.0 

57 

1.95 

7.7 

24 

255 

190 

4* 

12.5 

66 

1.98 

7.9 

30 

370 

275 

5 

15.0 

80 

2.00 

8.0 

36 

500 

375 

6 

19.0 

100 

2.05 

8.2 

42 

665 

500 

7 

24.0 

125 

2.10 

8.4 

48 

850 

635 

8 

29.0 

155 

2.15 

8.6 

54 

1,050 

775 

9 

34.0 

180 

2.19 

8.8 

60 

1,300 

970 

10 

41.0 

220 

2.21 

8.9 

72 

1,575 

1,200 

11 

46.0 

250 

2.24 

9.0 

84 

1,850 

1,400 

12 

51.0 

275 

2.32 

9.3 

Electrolyte 

is the 

name 

given 

to the 

solution used 


in storage batteries and other batteries. 


Electromagnets.—The magnetic flux is equal to 
the magnetomotive force divided by the reluctance. 
The magnetomotive force is the product of current 
times number of turns of wire and is known as 
ampere turns. The reluctance of the iron of all well 
designed magnets is very low but that of the air gap 
is high, so that roughly speaking we can judge the 
total reluctance by the air gap. In any given case 
the magnetic flux is approximately proportional to 
the current strength up to a point at which the iron 


ELECTRICAL TABLES AND DATA 


58 


becomes nearly saturated. After this the increase 
is slow until the point of full saturation is reached 
and after this it is very slow. 

To increase the magnetization (e. m.f. being fixed) 

I we must increase the size of wire; winding more turns 
of the same wire upon a spool simply decreases the 
current required for a given magnetization but does 
not alter the magnetization itself. The self-induction 
and the sparking are proportional to the square of 
the number of turns of wire. The heating is pro¬ 
portional to the square of the current used. The 
heating of the coils sets the limit of the current 
which may be used. A radiating surface of from 
1 to 3 square inches per watt consumed in the coil is 
usually provided. One watt per square inch will 
heat the coil very much if it is in use continuously. 
The possible traction of electromagnets is about 
200 lbs. per square inch for good annealed wrought 
iron, and 75 for cast iron. This, however, varies 
widely with the quality of iron used. In laboratory 
experiments as high as 1,000 lbs. per square inch 
has been obtained. Single phase a-c. magnets do 
not give a constant pull but two and three phase 
magnets are very serviceable. The “chattering’’ of 
single phase magnets can be lessened by a “shading 
coil.” Lifting magnets are extensively used. They 
are built with the two poles concentric and the 
material to be lifted constitutes the armature. Per¬ 
manent magnets are used only in small sizes. 

USEFUL FORMULAS AND TABLES 

In the following formulas it is assumed that the 
wires lie squarely over one another in the coil, each 
wire fully occupying a space equal to the square of 
its diameter. As in most coils some insulating me¬ 
dium is placed between the different layers, this is 
about the condition which exists in practice. 



60 


ELECTRICAL TABLES AND DATA 


The symbols used in the formulas are as follows: 

d = diameter of wire, in inches, over insulation. 

I = length of wire, on spool, in inches. 

nt = number of turns. 

r= resistance of one foot of wire. 

rs= radiating surface. 

B = diameter of core and insulation, in inches. 

D = diameter over outside of completed winding, 
in inches. 

L = length of winding space on spool, in inches. 

N = depth of winding from core to outside, in 
inches. 

W = weight of wire. 

a, c y k = constants for use in the formula, given in the 
tables below. Each constant has a different 
value for each size and kind of wire used. 

Number of turns in a given spool (see Figure 5) : 


1 - 

- 7 

c 

c ^- 

z 

M/ 

- —' 


... 

,HnTmintt7rH.il 

t- - ^ - - 

D DQ 



✓ 



jyi 

k v 

*- L ^ 

IHiM 


Figure 5. 


nt = 


LxN 

d 2 


Diameter of wire to give a certain number of turns: 


d 


-v 


LxN 
n t 
























ELECTRICAL TABLES AND DATA 


61 


Cross-section of winding space, or LxN, necessary 
to accommodate a certain n amber of turns of a given 
wire: 


LxN = d 2 xnt. 

Length of wire on a given spool: 

1= (D 2 - B 2 ) Lxk. See table below for value of k. 
Weight of wire on a given spool: 

W = ( D 2 -B 2 ) Lxc. See table below for value of c. 
Resistance of wire on a given spool: 

R= (D 2 - B 2 ) Lx a. See table below for value of a. 
Radiating surface for a given spool: 
rs-D x3.14xL. 




Ir 


TABLE XVn 

CONSTANTS. 




r i 

Constant for Length 

t -^--\ /- c* -> 

Constant for Weight Constant for Resistance 

© 

to 

P 

a 

fl 

o 

•M 

o 

0 

o 

+-> 


c _. 

o S 

o 

4-» 4^ u 

O 

C 

o 

«*-> 

o 

fl 

o 

4-» 


U 

O 

o 

O 

•H 

TO 

O o ~ 

^ O TO 

o 

O 

O 

4-4 

TO 

TO 

Q) 

© 

© 

^ 0> V 

0) 

<D 

© 


•Q 

•—» 
to 

to 

’S to to 

£> 

p 

to 

to 


o 

c 

c 

o c a 

O 

a 

c 

« 

Q 

•H 

TO 

TO 

Q TO TO 

Q 

•—4 

TO 

TO 

20 

40.9 

50.4 

56.7 

.137 .162 .177 

.415 

.512 

.576 

21 

50.4 

64.1 

72.7 


.638 

.812 

.920 

22 

60.2 

78.0 

89.7 


.97 

1.257 

1.445 

23 

68.8 

89.7 

104.7 


1.387 

1.82 

2.08 

24 

83.6 

113.5 

135. 

.1115 .149 .169 

2.14 

2.91 

3.46 

25 

97.2 

135. 

163. 


3.14 

4.36 

5.27 

26 

114. 

163. 

202. 


4.65 

6.65 

8.24 

27 

135. 

202. 

255. 


6.94 

11.75 

13.1 

28 

148. 

226. 

291. 

.0845 .122 .148 

9.60 

14.62 

18.82 

29 

182. 

291. 

387. 


14.85 

23.7 

31.6 

30 

201. 

334. 

454. 


20.7 

34.4 

46.8 

31 

226. 

387. 

542. 


29.36 

50.25 

70.4 

32 

255. 

454. 

655. 

.0687 .1045.132 

41.8 

74.4 

107.2 

33 

291. 

542. 

812. 


60.33 

114.5 

168. 

34 

334. 

655. 

1023. 


87.1 

170.5 

266.5 

35 

354. 

712. 

1140. 


116.2 

234. 

374.8 

36 

387. 

811. 

1340. 

.0492 .0825.1115 

160. 

335.5 

555. 

37 

422. 

897. 

1582. 


220.5 

468. 

806. 

38 

457. 

1023. 

1825. 


308. 

674. 

1192. 

39 

496. 

1170. 

2165. 


412. 

972. 

1795. 

40 

532. 

1300. 

2525. 

.038 .0615 .0888 

557. 

1360. 

2645. 












<32 

ra 

©eg 

N . 

am 

0 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 


ELECTRICAL TABLES AND DATA 


TABLE XVin 

Round Cotton-covered Magnet Wire 
American Steel & Wire Co. 
Coarse Sizes 


Single Cotton 


Double Cotton 


Diametei 

Inches 

Allowable 
Variation 
Either 
Way in 
Per Cent. 

Rated 
Area 
in Cir. 
Mils. 

Covered Approxi¬ 
mate Values 
Outside Feet 
Diameter per 
Inches Pound 

Covered Approx¬ 
imate Values 
Outside Feet 
Diameter per 
Inches Pound 

0.3249 

i of 1 

105,625 

.333 

3.1 

.339 

3.1 

.2893 

$ of 1 

83,694 

.297 

3.9 

.303 

3.9 

.2576 

a of i 

66,358 

.266 

5. 

.272 

4.9 

.2294 

f of 1 

52,624 

.237 

6.2 

.243 

6.2 

.2043 

a of 1 

41,738 

.212 

7.8 

.218 

7.8 

. .1819 

f of 1 

33,088 

.190 

9.9 

.196 

9.9 

.1620 

Jof 1 

26,244 

.170 

12.5 

.176 

12.4 

.1443 

Jof 1 

20,822 

.152 

15.7 

.158 

15.6 

.1285 

1 

16,512 

.136 

19.8 

.142 

19.6 

.1144 

1 

13,087 

.121 

24.9 

.125 

24.7 

.1019 

1 

10,384 

.108 

31.4 

.113 

31.1 

.0907 

1 

8,226 

.097 

39.5 

.102 

39.1 

.0808 

1 * 

6,528 

.087 

49.6 

.092 

49.2 

.0720 

u 

5,184 

.078 

62.5 

.083 

61.7 

.0641 

11 

4,108 

.070 

78.6 

.075 

77.5 

.0571 

1 * 

3,260 

.063 

98.9 

.068 

97 

.0508 

1* 

2,580 

.056 

125 

.060 

122 

.0453 

1 * 

2,052 

.050 

157 

.054 

153 

.0403 

U 

1,624 

.045 

198 

.050 

192 

.0359 

If 

1,288 

.041 

248 

.045 

240 


ELECTRICAL TABLES AND DATA 


63 


ENAMELED MAGNET WIRE 

Enamel insulation has a dielectric strength far in 
excess of silk or cotton covered wire. It will also 
withstand a much greater heat, as silk and cotton 
insulation will char at 270° Fahr., whereas enamel 
insulation will withstand 450° Fahr. without the 
slightest deterioration. 

Another decided feature about enamel insulation 
is the economy of space where this material is used 
for coil windings, and it takes up much less space 
than the single silk insulation. This feature is a 
very important one, especially to manufacturers of 
electrical instruments and apparatus where space 
economy is essential. 


TABLE XIX 


®C8 

Diam. 

Enam. 

Approx. 

Feet 

Approx. 
Turns per 

Size 

Dlam. 

Enam. 

Approx. 

Feet 

Approx. 
Turns per 

02 PQ 

Wire 

per Lb. 

Sq. In. 

B. &S. 

Wire 

per Lb. 

Sq. In. 

16 

• • • • 

126 

359 

29 

.0122 

2570 

7900 

17 

• • • • 

159 

447 

30 

.0109 

3240 

10000 

18 

»<• • • 

201 

567 

31 

.0097 

4082 

12620 

19 

• • • • 

253 

715 

32 

.0087 

5132 

16020 

20 

.0337 

320 

885 

33 

.0077 

6445 

20400 

21 

.0302 

404 

1126 

34 

.0069 

8093 

25200 

22 

.0269 

509 

1400 

35 

.0062 

10197 

31900 

23 

.0241 

642 

1736 

36 

.0055 

12813 

40000 

24 

.0215 

810 

2160 

37 

.0049 

16110 

51600 

25 

.0192 

1019 

2770 

38 

.0044 

20274 

65700 

26 

.0171 

1286 

3460 

39 

.0039 

25519 

81600 

27 

.0153 

1620 

4270 

40 

.0035 

32107 

104000 

28 

.0136 

2042 

5400 

• • 

• • t • 

• • • • 

• • • • 


64 


ELECTRICAL TABLES AND DATA 


TABLE XX 


Table for Insulated Copper Wire. (Belden Manufacturing Co.) 


Single Cotton, Double Cotton, Single Silk, Double Silk, 
Total Insulation Total Insulation Total Insulation Total Insulation 


r/i m 

Thickness 

4 Mils. 

Thickness 

8 Mils. 

Thickness 

1% Mils. 

Thickness 

4 Mils. 

B. & l 
Gaug< 

Ohms Feet Ohms 

per per per 

pound pound pound 

Feet 

per 

pound 

Ohms 

per 

pound 

Feet 

per 

. pound 

Ohms 

per 

pound 

Feet 

per 

pound 

20 

3.15 

311 

3.02 

298 

3.24 

319 

3.18 

312 

21 

4.99 

389 

4.72 

370 

5.12 

403 

5.03 

389 

22 

7.88 

488 

7.44 

461 

8.15 

503 

7.96 

493 

23 

12.44 

612 

11.7 

584 

12.92 

636 

12.65 

631 

24 

19.55 

762 

18.25 

745 

20.50 

800 

19.95 

779 

25 

30.8 

957 

28.45 

903 

32.50 

1005 

31.5 

966 

26 

48.6 

1192 

44.3 

1118 

51.29 

1265 

49.7 

1202 

27 

76.45 

1488 

68.8 

1422 

82.00 

1590 

78.3 

1542 

28 

120 . 

1852 

106.5 

1759 

129.00 

1972 

123.5 

1917 

29 

188.5 

2375 

164. 

2207 

205.00 

2570 

194. 

2485 

30 

294.6 

2860 

252. 

2534 

328.5 

3145 

306.5 

2909 

31 

460.5 

3800 

384.5 

2768 

512.3 

3943 

477. 

3683 

32 

716. 

4375 

585. 

3737 

810.0 

4950 

747. 

4654 

33 

1117. 

5390 

880. 

4697 

1277.5 

6180 

1165. 

5689 

34 

1720. 

6580 

1315. 

6168 

2018. 

7740 

1810. 

7111 

35 

2642. 

8050 

1960. 

6737 

3175. 

9680 

2820. 

8534 

36 

4060. 

9820 

2890. 

7877 

4970. 

12000 

4340. 

10039 

37 

6190. 

11860 

4230. 

9309 

7940. 

15000 

6660. 

10666 

38 

9440. 

14300 

6150. 

10666 12320. 

18660 10250. 

14222 

39 

14420. 

17130 

8850. 

11907 19200. 

23150 15600. 

16516 

40 

22600. 

21590 12500. 

14222 30200. 

28700 23650. 

21333 


ELECTRICAL TABLES AND DATA 


65 


TABLE XXI 

Table of Diameters (d) and Square of Diameters (d 2 ) for 

Insulated Copper Wire. 


B. & S. Double Cotton Single Cotton 


Single Silk 



d 

d 2 

d 

d2 

d 

d 2 

20 

.040 

.0016 

.036 

.001296 

.034 

.001156 

21 

.036 

.0013 

.032 

.00102 

.030 

.0009 

22 

.033 

.00109 

.029 

.00084 

.027 

.00073 

23 

.031 

.00096 

.027 

.00073 

.025 

.000625 

24 

.028 

.000784 

.024 

.000576 

.022 

.000484 

25 

.026 

.000675 

.022 

.000484 

.020 

.0004 

26 

.024 

.000575 

.020 

.0004 

.018 

.000324 

27 

.022 

.000484 

.018 

.000324 

.016 

.000256 

28 

.021 

.000441 

.017 

.000289 

.015 

.000225 

29 

.019 

.00036 

.015 

.000225 

.013 

.000169 

30 

.018 

.000324 

.014 

.000196 

.012 

.000144 

31 

.017 

.000289 

.013 

.000169 

.011 

.000121 

32 

.016 

.000256 

.012 

.000144 

.010 

.000100 

33 

.015 

.000225 

.011 

.000121 

.009 

.000081 

34 

.014 

.000196 

.010 

.000100 

.008 

.000064 

35 

.0136 

.000185 

.0096 

.000092 

.0076 

.0000576 

36 

.013 

.000169 

.009 

.000081 

.007 

.000049 

37 

.0124 

.000155 

.00845 

.000073 

.00645 

.0000415 

38 

.012 

.000143 

.008 

.000064 

.006 

.0000362 

39 

.0115 

.000132 

.0075 

.000056 

.0055 

.0000303 

40 

.0111 

.000123 

.0071 

.0000504 

.0051 

.000026 


66 


ELECTRICAL TABLES AND DATA 


Elevators. —Electric motors are used direct con¬ 
nected or belted; in some cases they are used to 
pump water for hydraulic elevators. Motors should 
be capable of exerting a strong starting torque, and 
are generally compounded. Means are usually pro¬ 
vided for cutting out the compound winding, or 
otherwise weakening the field to obtain high speeds. 
To prevent sparking at the brushes, commutating 
poles are frequently used. The ordinary commer¬ 
cial motor is seldom used for elevator service. 

The methods of speed control with d. c. motors 
consist in weakening the field and cutting resistance 
out or in; dynamic braking is also used in some 
cases for slowing down. With a. c. motors wound 
rotors are often used. 

Single phase as well as two and three phase motors 
are practicable, and variable speed motors are often 
employed. Hydraulic elevators require about 1.7 as 
much power as direct connected. A.-c. elevator 
motors under the same conditions require about 20 
to 30 per cent more power than d. c. motors. 

The H. P. required can be found by the formula 

TT P lxS 

33,000xe 

where 1 = unbalanced load in pounds, 5 = speed in feet 
per minute, e- combined efficiency of motor and ele¬ 
vator machinery. This is usually about 0.50. 

The speed of freight elevators often runs as low 
as 65 to 85 feet per minute, while some passenger 
elevators run as fast as 700 feet per minute. As 
the load is always intermittent motors may be rated 
high, and the starting torque is from two to two 
and one-half times running torque. 

The following table gives the H. P. required to lift 
various loads at speeds given; a combined efficiency 
of 50 per cent being assumed. 



ELECTRICAL TABLES AND DATA 


67 


TABLE XXII 


Table. showing H. P. required to lift unbalanced loads at 
speeds given. Efficiency of 50 per cent assumed. 


Speed in Feet 


Lbs. 

75 

100 

125 

150 

1000.... 

4.5 

6.1 

7.6 

9.1 

1250.... 

5.7 

7.6 

9.5 

11.4 

1500.... 

6.8 

9.1 

11.4 

13.6 

1750.... 

7.9 

10.5 

13.3 

15.8 

2000.... 

9.1 

12.1 

15.2 

18.2 

2500.... 

11.3 

15.1 

19.0 

22.6 

3000.... 

13.6 

18.2 

23.7 

27.2 

3500.... 

15.9 

21.2 

27.5 

31.8 

4000.... 

18.2 

24.2 

30.4 

36.4 

4500.... 

20.4 

27.3 

34.2 

40.8 

5000.... 

22.7 

30.3 

38.0 

45.4 

6000.... 

27.2 

36.4 

45.4 

54.4 


Per Minute 


200 

250 

300 

400 

500 

12.1 

15.1 

18.2 

24.2 

30.2 

15.2 

19.0 

22.8 

30.4 

38.0 

18.2 

22.8 

27.2 

36.4 

45.6 

21.0 

26.6 

31.6 

42.0 

53.2 

24.2 

30.4 

36.4 

48.4 

60.8 

30.2 

38.0 

45.2 

60.4 

76.0 

36.4 

47.4 

54.4 

72.8 

94.8 

42.4 

55.0 

63.6 

84.8 

110.0 

48.4 

60.8 

72.8 

96.8 

121.6 

54.6 

68.4 

81.6 

109.2 

136.8 

60.6 

76.0 

90.8 

121.2 

152.0 

72.8 

90.8 

108.8 

145.6 

181.6 


Emergency Lighting. —This is usually required in 
churches, theatres and other places where large num¬ 
bers of people congregate. The purpose is to pro¬ 
vide a system of illumination which shall be in 
service if the main system should fail. In large 
cities the emergency lighting is supposed to be used 
during the entire time the audience is in the build¬ 
ing. An entirely independent and separate service 
should be provided for it, and there should be no 
switches or fuses except those absolutely necessary. 

Equalizers. —Equalizer wires are used in connec¬ 
tion with two or more compound generators operated 
in parallel. All connections must be to the same 
terminal with series field. Wires should be led to 
switchboard, and connected to middle blade of 
switch. Arrange switch blades so that equalizer 
will be connected slightly ahead of other wire. 
The lower the resistance of the equalizer, the closer 
will be the regulation of the machines. Never con¬ 
nect ammeter on same side with equalizer. 



68 ELECTRICAL TABLES AND DATA 

Factors.— Assurance Factor. —This is the ratio of 
the voltage at which a wire or cable is tested to that 
at which it is to be used. 

Demand Factor. (See Demand Factor ).—This is 
the ratio or the maximum demand of any system, or 
part of a system, to the total connected load of the 
system, or of the part of the system under consider¬ 
ation. 

Diversity Factor. —The diversity factor of any 
part of a system of distribution is the ratio of the 
sum of the maxima of the subdivisions to the maxi¬ 
mum demand on the source of supply during some 
given time. 

To find the diversity factor we divide the sum of 
the maxima of the consumers during a given period 
of time by the maximum registered at the source of 
supply during the same time. If all consumers use 
their maximum energy at the same instant the diver¬ 
sity factor is 1. A large diversity factor is a dis¬ 
tinct advantage. In a central station system a cer¬ 
tain diversity factor will be found to exist between 
the consumers maxima, and the transformer serving 
them; between the various transformers and the 
main serving them there will be another diversity 
factor; between the mains and their feeder still 
another will exist, and so on between mains, sub¬ 
stations, transmission lines, and central station. The 
diversity factor of the last station is found by multi¬ 
plying together all the other diversity factors. 

Average diversity factors for a large central sta¬ 
tions as given by Gear & Williams are: 

Residence lighting. Diversity factor from 3.32 to 
3.40. Commercial lighting. Diversity factor from 
1.40 to 1.51. General power. Diversity factor from 
1.39 to 1.60. 

Load Factor. —The load factor is the ratio of the 
average load to the maximum load demanded by a 


ELECTRICAL TABLES AND DATA 


69 


consumer, a group of consumers connected to a sin¬ 
gle transformer, a group of transformers, feeders, 
mains, transmission lines, substations, generators, or 
central stations. For each of these on the same sys¬ 
tem it has a different value which is found by divid¬ 
ing the average load by the maximum load. A low 
load factor is a disadvantage. 

The following data are condensed from tables pub¬ 
lished by Gear & Williams in “Electric Central Sta¬ 
tion Distributing Systems.” 

Residence lighting. 

Individual consumer’s average load factor = 7%. 

Transformer load factor = 23% to 24%. 

Commercial lighting. 

Average consumer’s load factor = 10% to 13%. 

Transformer load factor = 15% to 19%. 

General power. 

Average consumer’s load factor = 15% to 21%. 

Transformer load factor=21% to 30%. 

Plant Factor .—This is the ratio of the average load 
to the rated capacity of the power plant. 

Power Factor .—The power factor is the ratio of 
the true power to the volt-amperes. In the case of 
sinusoidal voltage and current, the power factor is 
equal to the cosine of their difference in phase. The 
power factor is always less than unity and may be 
either lagging or leading. 

Reactance Factor .—This is the ratio existing be¬ 
tween the reactance of a circuit, and its ohmic resist¬ 
ance. 

Reactive Factor .—The reactive factor expresses 
the ratio of the wattless volt-amperes to the total 
volt-amperes. It is equal to the reactance divided by 
the impedance, which is equal to the sine of the 
angle between the impressed voltage and the current. 

Safety Factor .—The ratio of the strength of ma¬ 
terial to the load to which it is to be subjected. It is 


70 


ELECTRICAL TABLES AND DATA 


common practice to use a safety factor of 4 or 5. 

Saturation Factor .—The saturation factor of a ma¬ 
chine is the ratio of a small percentage increase in 
the field excitation, to the corresponding increase in 
voltage thereby produced. 

Factories.—It is an old custom to illuminate fac¬ 
tories by means of small c. p. lamps distributed among 
machinery so as to give each workman in need of it 
one lamp. Since the advent of the large wattage 
tungsten, or Mazda lamps, this has been somewhat 
changed. The change has been further helped along 
by individual drive machinery which has eliminated 
the belting and shafting. Where the work is not 
particular, one 100 watt tungsten lamp, if kept clean, 
to every 200 or 300 square feet of floor surface will 
give good results. Where particular work is done 
this illumination must be helped out by a 15 watt 
local lamp. A general illumination has the advan¬ 
tage that it will not have to be changed every time a 
machine is moved, which frequently happens. Where 
individual lighting for machinery is to be provided 
it will be well to avoid placing lamps before the 
machinery is located; plans are seldom reliable. The 
mercury vapor lamp gives a very serviceable illumin¬ 
ation for some purposes, but it is said that fine ma¬ 
chine work is not well done under it; also because of 
the ghastly appearance is gives faces, many men do 
not like to work under it. Oil dissolves rubber very 
fast, and when flexible cord is used around machinery 
it is well to encase it in loom. 

To avoid interference with open wires run them as 
far as possible between joists or along beams. Drop 
all lights from ceiling and never use floor pockets or 
side wall outlets. Make ample provision for glue 
pots and small portable motors. 

(For hints on motors, see Motors.) 

Fans.— (See Ventilation.) 


ELECTRICAL TABLES AND DATA 


71 


Farad. —The practical unit of capacity. A con¬ 
denser or conductor in which a charge of one coulomb 
(1 ampere for 1 second) produces a p.d. of one volt 
has a capacity of one farad. The farad is much too 
large for practical work, and micro-farads are used. 
A condensor of two or three micro-farads is quite 
large. 

Faradic Current. —This term is used in therapeu¬ 
tics, and designates the current taken from an induc¬ 
tion coil as distinguished from a galvanic or direct 
current. 

Faure Plate. —In this type of storage battery plate, 
the active material is pasted onto the supporting 
material, instead of being formed there. This type 
of plate is used mostly for vehicles. It gives a maxi¬ 
mum of capacity with a minimum of weight. 

Feeders. —These are the wires which start from a 
central station, substation, or other center and feed a 
group or center from which mains supply translating 
devices. The term is always rather loosely used. 
There may be feeders and sub-feeders. A voltage of 
about 1,000 per mile of feeder length is customary. 

Festoons.—Festoons to be strung across streets are 
usually wired with number 8 or 10 wire, and weather¬ 
proof sockets. As a rule they are supported in the 
center of the street, and swung from pulleys which 
allow of lowering for lamp renewals, etc. In order 
to allow for graceful hanging the wires should be 
from 1.3 to 1.6 times the width of street. Lights are 
usually spaced from 18 inches to two feet apart. At 
street intersections two festoons are often swung 
diagonally across, and in such a case the length of 
wire should be two times the width of street. The 
supporting cables from which the festoons are swung 
are attached to buildings and poles on opposite side 
of street and in many cases they must be run diag¬ 
onally to find attachments which will allow the fes- 


72 ELECTRICAL TABLES AND DATA 

toon to come in its proper place. This often necessi¬ 
tates very long spans and requires strong cables. 
Three-eighths and half-inch steel cables are often 
used. Where festoons are swung over trolley lines 
strain insulators are used. Festoons for theatre 
work are made up of stage cable and weatherproof 
sockets; joints are staggered, and taped to prevent 
strain on joints. 

Fiber. —This, in general, is a serviceable insulating 
material, but on account of the fact that it does not 
resist moisture, and swells and warps when wet, it 
is not approved for light and power voltages. 

Field.—This term describes either a magnetic, or 
an electrostatic field. Field magnets are the electro¬ 
magnets which produce the electric field in which the 
armature revolves. Field coils are the coils in which 
the magnetizing current circulates. A field rheostat 
is one which regulates the current in the field coils. 
A field of force is the space traversed by an electro¬ 
static, or magnetic flux. The field windings of induc¬ 
tion motors are those in which the rotating field is 
produced. 

Fire Alarms. —May he either automatically, or 
manually operated. In the manual system a glass 
disk is usually broken to send in an alarm. In the 
automatic system a fuse opens, or closes a circuit 
and sends in the alarm. A system in which the cur¬ 
rent is constantly flowing is always preferable be¬ 
cause it is always under test, and failure of any kind 
will send in an alarm. Means of testing without 
sending in alarms should be provided. The common 
fire alarm telegraph system consists of boxes con¬ 
taining notched wheels which are released when the 
box is pulled, and send in the code signal. 

Fish Work. —For light and power voltages ar¬ 
mored cable, or single rubber covered wires in cir¬ 
cular loom are used; never use twin wire. When 


ELECTRICAL TABLES AND DATA 


73 


one is alone on a fish job, a bell and battery con¬ 
nected to the fish wire with one pole, and to a coil 
of wire inserted in the hole at the other end with the 
other, is very useful. When the fish wire touches 
the other wire the bell will ring. Use a small chain 
for dropping and a spring wire for other work. 

Fixtures. —The height of hanging varies from 6 feet 
2 inches to 7 feet. The so-called art-domes are hung 
much lower, but they are a passing fad. 

Memorandum of Fixture Work 


Name. 

Address. 

Room or Circuit Number 







No. lights on each circuit. 






No. of beam lights. 







No. of electric lights. 







No. of gas lights. 







>h Style of finish. 







^3 Catalogue number. 







Sketch number. 







ri Kind of glassware. 







0 Catalogue number. 







Size of holders. 







Kind of sockets. 







Height lowest point above floor 
Size of gas stub. 












y ■ 







No. of elec, lights. 







o 

Kind of sockets. 







No. gas lights. 







-2 Stvle of finish. 







Catalogue number. 







« Sketch number. 







pq Kind of glassware. 







Catalogue number. 







Height above floor. 







Size gas stub. 







o 







No. switches. 







Kind of switch. 







Style of finish. 















































































74 ELECTRICAL TABLES AND DATA 

The standard height of brackets is from 5J to 6 
feet above floor. 

No fixture should ever be selected except with 
reference to the room in which it is to be hung, and 
it should be neither conspicuous for its expensiveness 
or cheapness. 

Elaborate fixtures made up of cheap material 
should never be used; pretense is always abomina¬ 
ble. Before installing, test each fixture for con¬ 
tinuity, short circuits and grounds; move wires while 



Figure 6.—Method of Tying Knots in Flexible Cord. 

testing. The following memoranda will be of use in 
ordering fixtures: 

Flashers on branch circuits usually operate single 
pole. In such a case one-half of the cut-outs may be 
located at flasher, the other half, if more convenient, 
in the sign. Although the flasher allows the use of 
only a part of the lights at a time, it is customary to 
run mains for the full requirements of all the lights. 

Flat Irons constitute a considerable fire hazard and 
every precaution should be taken to install them 
safely. A pilot lamp is very useful. Provide extra 
flexible cord to help out the cord furnished with iron 
so the two will be long enough to allow iron to fall 
to the floor without straining fixture or other attach¬ 
ment. The common domestic flat irons weighing 




ELECTRICAL TABLES AND DATA 


75 


from 3 to 8 lbs. require from 250 to 635 watts. A 
substantial metal stand should always be provided 
and should separate the iron about 2^ inches from 
cloth on board. 

Flexible Cord improperly used causes the majority 
of electrical fires. The common cord should always 
hang free in air; should never be spliced, and should 
be soldered only where it connects to line wires. In 
sockets, rosettes, and outlet boxes it must be knotted 
to prevent strain from coming on the joints. The 
best method of tying knots is shown in Figure 6. 

Foundries. —The general illumination of foundries 
is commonly effected by means of arc lamps or clus¬ 
ters of incandescent lamps. The flaming arc is very 
effective.* Strong shadows are useful, as all objects 
soon assume the same color. Cleaning of lamps is 
an important item and for this reason clusters of 
incandescent lamps are often encased in outer globes, 
which are more easily cleaned. In addition to the 
general illumination, each molder requires an indi¬ 
vidual lamp for his own use. 

Frequencies. —A frequency of 25 cycles per second 
is generally used for rotary converter work, and 
power transmission. Arc and incandescent lamps do 
not operate well with such low frequencies, hence a 
frequency of 60 cycles is generally used for illumina¬ 
tion. In any given circuit, the higher the frequency, 
the greater will be the reactance. If the frequency 
is too high for a given device the current will be 
insufficient, if too low it will be excessive. A fre¬ 
quency changer is a machine usually installed in 
substations. A frequency indicator is usually in¬ 
stalled upon switchboards, or used in connection 
with a large motor installation. 

Fuses. —Fuses are divided into three general 
classes: open, enclosed, and expulsion. The fuse 
metal itself is never hard enough to stand up well 


76 


ELECTRICAL TABLES AND DATA 


under binding screws, hence copper tips are neces¬ 
sary. If these are not used there will be much un¬ 
necessary blowing. All fuses should be placed in 
cabinets not only to prevent molten metal from caus¬ 
ing fires, but to insure greater reliability of the fuse 
by protecting it against drafts. The fusing of branch, 
and main circuits inside of buildings is thoroughly 
covered by the National Electrical Code. The rule in 
general is to provide fuse protection wherever the 
size of wire changes. The fuse to be of such size as 
to prevent current rise above the safe carrying ca¬ 
pacity of wires as given in the Code. Each motor or 
other translating device also requires separate fuse 
protection except that small devices aggregating not 
more than 660 watts capacity may be grouped under 
one fuse. 

All plans of fusing are a compromise between the 
desire to obtain adequate protection on the one hand, 
and escape the trouble caused by the many accidental 
breaks and uncalled for operations of fuses. 

Overhead systems as a rule are not fused where 
they leave the switchboard, but are equipped with 
switches or disconnectives. 

Feeders leaving the transmission lines are also 
usually left without fuse protection, but equipped 
with disconnectives. 

Fuse protection is fully demanded only where the 
chances of short circuits or grounds are quite great, 
and this point is not reached until the transformers 
are reached. It must be borne in mind that all con¬ 
sumers devices are protected by service fuses and 
switches, and these protect the outer lines fully 
against everything except what occurs on the poles. 
The primary side of transformers of small and me¬ 
dium capacity is usually protected by fuses, but the 
fuses are made large enough so that ordinary over¬ 
loads will not cause them to blow. 


ELECTRICAL TABLES AND DATA 


77 


TABLE XXIII 


The following table gives fuse sizes often used 
with transformers of the .capacities given. 


K.W. Capacity 

Size Fuse 

K.W. Capacity 

Size Fuse 


Amperes 

Amperes 

1 

3 

15 

15 

2 

3 

20 

15 

3 

3 

25 

20 

4 

3 

30 

20 

5 

5 

40 

30 

7 y 2 

10 

50 

40 

10 

10 




On the secondary side of transformers, fuses are 
not ordinarily used and it is not advisable to have 
them. In case a number of transformers feed a net¬ 
work the blowing of one fuse may cause the blowing 
of another, etc., until all are out. Under such cir¬ 
cumstances fuses cannot well be replaced until the 
load on the main is sufficiently reduced to allow one 
transformer to carry it, or until the feeder supplying 
the network has been opened; in this case the feeder 
must be left open until all fuses have been replaced. 
In connection with underground circuits the case is 
different. Here short circuits and grounds are much 
more likely to occur. Such systems also always sup¬ 
ply a much larger number of customers within a 
given space, and more care is necessary. Under¬ 
ground networks are usually fused at each junction 
point so that, if an overload causes one fuse to blow, 
the other will follow and clear the balance of the 
circuits from trouble. Wherever parallel lines are 
run they should be equipped with reverse current 
circuit breakers. Three phase four wire systems are 
usually provided with a single pole switch in each 
leg, thus any phase can be disconnected without in¬ 
terfering seriously with the others. For three phase 
three wire systems three pole switches are used. All 
telephone circuits should be protected by fuse and 


78 


ELECTRICAL TABLES AND DATA 


in addition with “sneak coils” and air gap arresters. 
Heat coils are arranged to open the circuit when a 
small or “sneak current” has passed through them 
for a considerable time, or a large current in an 
instant. Air gap arresters are supposed to open the 
circuit whenever unduly high potentials come to exist 
at their terminals. 


TABLE XXIV 


Tested Fuse Wire from % to 100 Ampere* 


Safe 

Best Lengths for Use 



Carrying 1 

and Fusing Cur¬ 

Length 

Mils. 

Capacity 

rents for such 

Per Lb. 

Dlam. 

Amperes 


Lengths 




Inches 

Amperes 

Ft. In. 


% 

1 

1% 

2550 

10 

% 

1 

2% 

1516 

13 

1 

lfc 

3 

993 

16 

2 

1% 

5 

407 

25 

3 

1% 

7 

265 

31 

4 

1% 

9 

207 

35 

5 

1% 

10 

167 

39 

6 

2 

12 

144 

42 

7 

2 

13 

120 

46 

8 

2 

15 

106 

49 

9 

2 

16 

94 

52 

10 

2y 4 

17 

84 

55 

12 

2t4 

20 

68 

61 

14 

2ti 

23 

58 

66 

15 

2y 4 

24 

55 

68 

16 

2y 2 

25 

49 

72 

18 

2 y 2 

28 

43 

77 

20 

2 y 2 

30 

37 10 

82 

25 

2% 

37 

28 9 

94 

30 

2% 

43 

24 

103 

35 

3 

49 

20 

113 

40 

3 

56 

17 2 

122 

45 

3 

62 

15 4 

129 

50 

3 

69 

13 6 

137 

60 

3t4 

81 

10 3 

158 

70 

3%‘ 

93 

8 10 

170 

75 

3 y 2 

99 

7 9 

182 

80 

3y 2 

106 

7 2 

189 

90 

3y 2 

118 

5 8 

212 

100 

4 

129 

5 

226 


ELECTRICAL TABLES AND DATA 


79 


Tested Fuse Strip from 50 to 600 Ampere* 


Safe 

Beat Lengths for Use 

Weight 

Carrying 

and Fusing Cur¬ 

Per Foot 

Capacity 

Amperes 

rents for such 

Length* 

Inches Ampere* 

Ounce* 

50 

3 

69 

1% 

60 

3% 

81 

1% 

70 

3% 

93 

1% 

75 

3% 

99 

1% 

80 

3%. 

106 

2 y 8 

90 

3% 

118 

2% 

100 

4 

129 

3 

125 

4% 

158 

3% 

150 

4% 

187 

4% 

175 

4y a 

215 

6 

200 

4% 

243 

6 V 8 

225 

4% 

270 

7% 

250 

4% 

298 

8 Vs 

275 

4% 

325 

9 % 

300 

5 

351 

10% 

350 

5% 

402 

12% 

400 

5 m 

450 

14% 

450 

5% 

500 

17 

500 

6 

550 

20% 

600 

ey 2 

675 

35 


The current required to fuse metals can be found 
by the well known Preece formula: 


/ = « V d z , 


where I = current in amperes, d = diameter of wire, 
and a - a constant for different kinds of metal as given 
below: 


Copper .10244 Iron 3148 

Aluminum .7585 Lead 1379 

German Silver.5230 








go ELECTRICAL TABLES AND DATA 

The table below is calculated from the above for¬ 
mula and constants, and gives the current required 
to fuse wires of various sizes. 


TABLE XXV 


B. & S. 

Copper 

Aluminum 

German 

Silver 

Iron 

Lead 

4 

942 

698 

481 

290 

127 

0 

666 

.493 

339 

204 

90 

8 

471 

349 

240 

145 

63 

10 

334 

247 

171 

103 

50 

12 

235 

174 

120 

72 

32 

14 

165 

122 

84 

51 

22 

16 

117 

86 

60 

35 

16 

18 

82 

60 

42 

25 

11 

20 

58 

43 

29 

18 

8 

21 

49 

36 

25 

15 

6 

22 

40 

29 

21 

12 

5 

23 

36 

26 

19 

11 

5 

24 

29 

21 

15 

9 

4 

25 

25 

18 

13 

8 

3 

26 

20 

15 

11 

<5 

3 

27 

17 

12 

9 

5 

2 

28 

14 

10 

7 

4 

2 

29 

12 

9 

6 

4 

1.5 

30 

10 

8 

5 

3 

1.2 

31 

8.5 

6 

4 

2.6 

1.0 

32 

7.0 

5 

4 

2.2 

0.9 

The 

range 

strands 
from No. 

of which 
26 to 36. 

flexible 

cord is 

made up 


Galvanic.—A term much used in therapeutics to 
denote continuous, or direct current. 




ELECTRICAL TABLES AND DATA 


81 


Garages. —The gasoline vapors so prevalent in 
garages do not ordinarily rise more than 4 feet above 
the floor. Avoid all possibility of electric sparks at 
this level, especially in pits. Electric lights should 
be well guarded with elastic lamp-guards which will 
protect the lamp against breakage even when it 
falls. 

Gas Lighting may be effected by pilot flame, a 
small quantity of sponge platinum on mantle, or by 
high-tension electric sparks jumping a number of 
spark gaps in the gas jets, or low-tension sparks 
applied to jets in multiple. A spark coil is required 
and it should be connected with a tell-tale relay and 
bell which will ring in case the system becomes 
grounded. Electric gas lighting wires must not be 
used on same fixtures with electric light. 

Gauges. —The American, or Brown & Sharp wire 
gauge, abbreviated respectively A. W. G. or B. & S. y 
is the one commonly used for measuring copper, 
aluminum, and resistance wires in general. The 
U. S. steel wire gauge is commonly used for steel 
and iron wire. This is also known as the Washburn 
and Moen; Roebling, and American Steel and Wire, 
and is generally abbreviated Stl. W. G. 

The Birmingham or Stubs’ Wire Gauge is some¬ 
times used for brass wire. It is commonly abbre¬ 
viated B. W. G. This, although spoken of as Stubs, 
is not identical with the Stubs’ Steel Wire Gauge.. 
The British Standard Wire Gauge, the Edison Wire 
Gauge and the Stubs’ Steel Wire Gauge are not much 
used in this country in electrical work. A compari¬ 
son of the different wire gauges is given below, 
diameters being given in mils (thousandths of an 
inch). 


82 


ELECTRICAL TABLES AND DATA 


CIRCULAR OF THE BUREAU OF STANDARDS 

TABLE XXVI 


Tabular Comparison of Wire Gauges. Diameters in Mils. 


• 

© 

fO 

s © 

a ta 

r> 03 

in be 

t—i <D 

o bn 
a> 

© 

be 

• 

o 

cj O 

.2 co 

CJ 

bn cs - 

•r-» ri 

"bn cs g 

H-> 2 

m * 

^5 fn e3 

o 

£ 

So 

§ 

O 

® ©°<3 

Steel ^ 
Gauge 1 

a o » 

• pH 

g.gj 

H 03 fl 

^.2 9 

5^6 

~ o 

% 2 

P »rH 

££ 

m o3rh 

;§§.§ 
6s £ 

© 

bo 

0 

ci 

O 

7-0 


490.0 




500. 

7-0 

6-0 


461.5 




464. 

6-0 

5-0 


430.5 




432. 

5-0 

4-0 

460. 

393.8 

454. 

454. 


400. 

4-0 

3-0 

410. 

362.5 

425. 

425. 


372. 

3-0 

2-0 

365. 

331.0 

380. 

380. 


348. 

2-0 

0 

325. 

306.5 

340. 

340. 


324. 

0 

1 

289. 

283.0 

300. 

300. 

227. 

300. 

1 

2 

258. 

262.5 

2S4. 

284. 

219. 

276. 

2 

3 

229. 

243.7 

259. 

259. 

212. 

252. 

3 

4 

204. 

225.3 

238. 

238. 

207. 

232. 

4 

5 

182. 

207.0 

220. 

220. 

204. 

212. 

5 

6 

162. 

192.0 

203. 

203. 

201. 

192. 

6 

7 

144. 

177.0 

180. 

180. 

199. 

176. 

7 

8 

128. 

162.0 

165. 

165. 

197. 

160. 

8 

9 

114. 

148.3 

148. 

148. 

194. 

144. 

9 

10 

102. 

135.0 

134. 

134. 

191. 

128. 

10 

11 

91. 

120.5 

120. 

120. 

188. 

116. 

11 

12 

81. 

105.5 

109. 

109. 

185. 

104. 

12 

13 

72. 

91.5 

95. 

95. 

1S2. 

92. 

13 

14 

64. 

80.0 

83. 

83. 

180. 

80. 

14 

15 

57. 

72.0 

72. 

72. 

178. 

72. 

15 

16 

51. 

62.5 

65. 

65. 

175. 

64. 

16 

17 

45. 

54.0 

58. 

58. 

172. 

56. 

17 

18 

40. 

47.5 

49. 

49. 

168. 

48. 

18 

19 

36. 

41.0 

42. 

40. 

164. 

40. 

19 

20 

32. 

34.8 

35. 

35. 

161. 

36. 

20 

21 

28.5 

31.7 

32. 

31.5 

157. 

32. 

21 

22 

25.3 

28.6 

28. 

29.5 

155. 

28. 

22 


ELECTRICAL TABLES AND DATA 


85 


• 

o 

eo<M 

© 

b-i 

CS be 

Gauge Ni 

American 
Wire Gau 
(B. & S.) 

Steel Wir 
Gauge 23 

Birmingh 
Wire Gau, 
(Stubs') 

23 

22.6 

25.8 

25. 

24 

20.1 

23.0 

22 . 

25 

17.9 

20.4 

20 . 

26 

15.9 

18.1 

. 18. 

27 

14.2 

17.3 

16. 

28 

12.6 

16.2 

14. 

29 

11.3 

15.0 

13. 

30 

10.0 

14.0 

12 . 

31 

8.9 

13.2 

10 . 

32 

8.0 

12.8 

9. 

33 

7.1 

11.8 

8 . 

34 

6.3 

10.4 

7. 

35 

5.6 

9.5 

5. 

36 

5.0 

9.0 

4. 

37 

4.5 

8.5 


38 

4.0 

8.0 


39 

3.5 

7.5 


40 

3.1 

7.0 


41 


0.6 


42 


6.2 


43 


6.0 


44 


5.8 


45 


5.5 


46 


5.2 


47 


5.0 


48 


4.8 


49 


4.6 


50 


4.4 



A © 

'a? © 

© 


Old Englis 
Wire Gaug 
(London) 

Stubs' Ste< 
Wire Gaug 

(British) 
Standard 
Wire Gaug 

d 

£ 

© 

bo 

3 

c« 

O 

27.0 

153. 

24. 

23 

25.0 

151. 

22 . 

24 

23.0 

148. 

20 . 

25 

20.5 

146. 

18. 

26 

18.75 

143. 

16.4 

27 

16.50 

139. 

14.8 

28 

15.50 

134. 

13.6 

29 

13.75 

127. 

12.4 

30 

12.25 

120 . 

11.6 

31 

11.25 

115. 

10.8 

32 

10.25 

112 . 

10.0 

33 

9.50 

no. 

9.2 

34 

9.00 

108. 

8.4 

35 

7.50 

106. 

7.6 

36 

6.50 

103. 

6.8 

37 

5.75 

101 . 

6.0 

38 

5.00 

99. 

5.2 

30 

4.50 

97. 

4.8 

40 


95. 

4.4 

41 


92. 

4.0 

42 


88. 

3.6 

43 


85. 

3.2 

44 


81. 

2.8 

45 


79. 

2.4 

46 


77. 

2.0 

47 


75. 

1.6 

48 


72. 

1.2 

49 


69. 

1.0 

50 


The American Wire Gauge sizes have here been rounded off 
to about the usual limits of commercial accuracy. 

The Steel W?ire Gauge is the same gauge which has been 
known by the various names: “Washburn and Moen, ,; 
“Koebling," “American Steel and Wire Co.'s. M Its abbre¬ 
viation should be written “Stl. W. G.,” to distinguish.it from 
“S. W. G. f ” the usual abbreviation for the (British) Stand¬ 
ard Wire Gauge. 


S4 ELECTRICAL TABLES AND DATA 

Generators. —Alternating Current generators may 
be of the revolving field or revolving armature type. 
The revolving field type is easier to insulate and less 
troublesome to maintain, hence is most widely used. 
There is another, known as an inductor type, in which 
usually all electrical parts are stationery and an iron 
spider is caused to revolve, it being so arranged as 
alternately and regularly to alter the magnetic flux 
and thus cause induction of e. m. f. This type is not 
much used. 

The so-called Induction generator is another type, 
and is similar to an induction motor; in fact, an 
induction motor, when driven above the speed of 
synchronism becomes an induction generator, and 
delivers current to the line. This type of generator 
cannot operate unless other alternators provide it 
with the necessary exciting current. The capacity in 
generators for field excitation must be nearly equal 
to one-third of the capacity of the induction gener¬ 
ators. This type of generator is well suited for fluc¬ 
tuating speeds such as are given by gas engines, but 
it can never constitute an entire plant. Alternating 
current generators are made to operate single-phase, 
two-phase and three-phase. The single-phase machine 
is not well suited for power work, and is more expen¬ 
sive per unit of output than polyphase machines. 
The two-phase generators are, as a rule, used only 
on old direct current installations which have been 
adapted to a.-c. operation. The three-phase system 
is the most economical and is almost universally used. 
It is well suited for either light or power transmission. 
Alternators may be built to be self-exciting, but this 
is not often done. Most of them require a direct 
current exciter. 

Efficiency .—Approximate efficiencies of generators 
of various sizes are given about as follows: 100 
K. V. A., 91 per cent; 500, 94; 1,000, 95; 2,000, 96; 


ELECTRICAL TABLES AND DATA 


85 


3,000, 96 to 97; 5,000, 97 or better. These efficiencies 
vary of course with the power factor, load, voltage, 
etc. 

Frequency. —The common frequencies are 25 and 
60 cycles per second, the lower being used for trans¬ 
mission to substations and for power alone. The 
higher frequency is used for mixed lighting and 
power, and also for lighting alone. In a single-phase 
machine the current and voltage per phase have but 
one meaning. The power is equal to IxE xpower 
factor, and the product of volts and amperes gives 
the volt-ampere rating of the machine. In a two- 
phase alternator each half supplies half of the cur¬ 
rent and power. The usual four transmission wires 
are sometimes combined into three wires, and in such 
a case the voltage between the two outside wires is 
1.41 times the phase voltage, and the current in the 
middle wire is 1.41 times the current in the outside 
wires. The power in such a combination may be 
found in two ways. Measuring current in the middle 
wire and the voltage across both phases, the power is 
equal to IxE xpower factor. Measuring current in 
one of the outside wires, and using phase voltage, the 
power is equal to IxE x2x power factor. Three- 
phase generators are always connected by means of 
3 main wires, and sometimes a neutral, but may be 
either delta or star. If the delta connection is used, 
the phase voltage is the same as the voltage between 
any two wires, but the current in any phase is 1.73 
times the current in any one of the wires. If the star 
connection is used, the voltage between any two wires 
is 1.73 times the voltage of any phase winding, and 
the current to deliver the same power will be only 
0.58 of the former current in the line wires. The 
power with either connection is equal to IxEx 1.73x 
power factor. 

Frequencies .—The common frequencies are 60 and 


86 


ELECTRICAL TABLES AND DATA 


25 cycles. The higher frequency is used for light, 
and mixed light and power loads. The lower is used 
for power alone and also for transmission lines to 
substations or converters. The frequency of any gen¬ 
erator depends upon the speed and number of poles 
and may be found by the formula: 

^ r. p.m. number of poles 
60 X 2 

The table below shows the speeds at which gener¬ 
ators provided with a certain number of poles must 
operate to deliver current at the frequencies given. 

TABLE XXVII 


60 Cycles. 


No. Poles. 

... 4 

8 

12 

16 

20 

24 

B. P. M. 

,...1,800 

900 

600 

450 

360 

300 



25 Cycles. 




No. Poles. 

.. . 4 

8 

12 

16 

20 

24 

B. P. M. 

,... 750 

375 

250 

187y 2 

150 

125 

Operation 

of Alternators 

in 

Parallel.- 

-In 

order 


that alternators may be operated in parallel they 
must be identical in four respects. The frequency 
must be the same. The voltage must be the same. 
The current and voltages must be in phase, i.e., their 
maxima and minima must occur at the same instant. 
The wave form of the machines should be as near as 
possible alike. 

The frequency is governed by the speed, and if it 
is not correct, the speed must be adjusted either by 









ELECTRICAL TABLES AND DATA 


87 


adjusting the engine, or diameters of pulleys. The 
voltage can be determined by a voltmeter test. 

Whether the machines are in or out of phase can 
be determined only by properly connected synchroniz¬ 
ing lamps, or synchronizing instruments. 

The synchronizing and keeping in step of alter¬ 
nators will be made easier by synchronizing the piston 
strokes of engines as far as possible if they are sepa¬ 
rately driven, or, if driven from a common shaft, by 
running one of the machines with a slack belt, which 
will allow it to fall in step more readily. Where 
synchroscopes are used the pointer will indicate which 
machine is running too fast or too slow: Where the 
synchronizing is done with lamps they may be con¬ 
nected so as to indicate synchronism either by dark¬ 
ness or light. If the machines are not in phase there 
will be alternations of darkness and light in the lamps 
which will alternate with great rapidity if the ma¬ 
chines are much out of synchronism, but will be at 
longer and longer intervals as they are brought more 
nearly into step. The proper time to close the switch 
is just a moment before the period of full darkness. 
If the machines are nearly in synchronism when 
thrown together, there will be cross current which 
will help to bring them together, but it is best to 
have them synchronized perfectly before connecting. 

The load cannot be divided among alternators by 
increasing the field excitation as with direct-current 
machines; it is necessary to give more steam to the 
engine of the light running generator. This tends to 
advance the generator and causes it to take more cur¬ 
rent. The power factor can be improved or altered 
by adjusting the field excitation. Adjust fields so 
that power factor of each machine is the same. 

Single Machine , Operation of .—See that machine 
is entirely disconnected from the load. Inspect all 
bearings and see that they are well oiled and that oil 


88 


ELECTRICAL TABLES AND DATA 


rings work property. Adjust field rheostat so thal 
all resistence is in circuit and close exciter circuit. 
Start machine, bringing it gradually up to speed and 
cutting out resistance in field rheostat until generator 
voltage comes to its proper value. Next throw in 
switches, bringing load on gradually if possible, and 
adjust rheostat to maintain voltage property. Test 
speed to see that it is at its proper value; the speed 
is of greater importance with alternators than with 
direct current generators. 

Rating .—For full details as to rating, the reader 
is referred to the Standardization Rules of the 
A. I. E. E., which are too lengthy to be given 
here. 

The maximum, or continuous, rating of an alter¬ 
nator is commonly taken as the load in kilowatts it 
can carry at 100 per cent power factor with a maxi¬ 
mum rise in temperature of any part of 50° C. 
(122° F.) above the surrounding air when that is 
25° C. (77° F). Corrections for other surrounding 
temperatures to be made according to A. I. E. E. 
Standardization Rules. Another rating, used mostly 
in connection wfith street railway work, allows a tem¬ 
perature rise of 45° C. (113° F.) under the same 
conditions as above, and requires that 50 per cent 
more than the rated load used for two hours shall not 
cause a temperature rise of more than 55° C. 
(131° F.). 

Voltage .—A voltage in excess of 12,000 or 13,000 is 
rarely generated direct; higher line voltages are ob¬ 
tained mostly by step-up transformers. 

Direct Current Generators , Compound Machines .— 
This is a combination of shunt and series dynamo, 
and a distinct improvement over the shunt machine. 
The compound winding can be adjusted to regulate 
the voltage as desired. It requires the same instru¬ 
ments as the shunt, and in addition heavy equalizing 


ELECTRICAL TABLES AND DATA 


S9 


wires run between each pair of machines. These 
should be carried to the board and the main switch 
should be triple pole. The machine may be connected 
either long shunt (shunt winding bridging compound 
fields as well as armature), or short shunt (shui.t 
field bridging only armature) ; it is merely a ques¬ 
tion of convenience. All these machines may be 
bi-polar or multi-polar, direct or belt connected and 
provided with commutating or interpoles. 

Rating .—Machines are commonly rated on the 
basis of their continuous output in kilowatts with a 
maximum rise in temperature of 50° C. (122° F.) 
above the surrounding air at 25° C. (77° F.). For 
full information see A. I. E. E. Standardization 
Rules. The common voltages are 110 volts for light¬ 
ing and small power (used mostly in isolated plants) ; 
220 to 250 also for lighting and power, but used 
mostly in larger plants, and for short distance dis¬ 
tribution ; 500 to 600 volts, used almost exclusively 
for street railway work; 2,000 to 6,000, or more, used 
for series arc lighting by direct current. 

The Series Machine is used only for constant cur¬ 
rent work. It requires the following instruments and 
fittings: 

Short circuiting switch for fields. 

Ammeter, a switchboard equipped with plugs and 
jacks. 

A polarity indicator is often advisable. 

The Shunt Machine is used for all variable current 
work. Its voltage regulation is poor, and requires 
constant attention. It requires a field rheostat, fuses, 
main switch or circuit breaker, volt meter, ammeter, 
ground detector, switchboard and pilot lamps. The 
voltage of this machine is variable and automatically 
decreases with an increase in the devices it supplies. 

Greek Alphabet. —Greek letters have become the 
standard symbols for many quantities dealt with in 


90 


ELECTRICAL TABLES AND DATA 


electrical and mechanical calculations. The letters 
and their pronunciations are given below: 


A a — Alpha. 

B /3 — Beta. 

T y — Gamma. 
A 8 — Delta. 

E c — Epsilon. 
Z £ — Zeta. 

H rj — Eta. 

® 0 — Theta. 


I i — Iota. 

K k — Kappa. 

A A — Lambda. 
M fji — Mu. 

N v —Nu. 

S £ — Xi. 

O cr—Omicron. 
n 7r — Pi. 


P p — Rho. 

2 o- — Sigma. 

T r — Tau. 

Y v — Upsilon. 
<t> <f> — Phi. 

X x —Chi. 

^ t ff — Psi. 

Q to — Omega. 


Gram or Gramme. —The gramme is the mass of a 
cubic centimeter of water at the temperature of its 
greatest density. It is the unit of mass and is equal 
to 15.43235 grains; 7,000 grains equal 1 lb. av. 

Gravity Cell .—This is a cell in which copper and 
zinc immersed in a solution of blue vitriol are the 
active elements. It is used for continuous work and 
where small constant currents only are required. 

Ground Detectors. —It is customary to provide 
ground detectors on all switchboards from which 
entirely insulated circuits are run. Tests should be 
made quite frequently, so as to catch a ground as soon 
as it comes on. When grounds exist on both, sides of 
a system, detectors are not reliable and the part to 
be tested must be disconnected from the board. Con¬ 
tinuously indicating detectors are preferable; static 
instruments are made which can be so used even an 
high voltage lines with perfect safety. 

Grounding. —Any connection of any part of a cur¬ 
rent carrying conductor, or live metal part of any 
device which has become connected to a foreign con¬ 
ducting medium so as to deliver current or potential 
to it, is spoken of as being grounded. Some devices 
and circuits are purposely grounded, the frame or 
the earth being relied upon as return conductors. 


ELECTRICAL TABLES AND DATA 


91 


The purposive grounding of wires used in connection 
with electrical work may be divided into two classes: 
The grounding of frames, conduits, etc., which are 
not supposed to become alive except through a break¬ 
down of the insulation, and the grounding of wires, 
or devices which usually do carry current. The life 
and fire hazard from electrical sources may be greatly 
reduced by improving the insulation, so that the 
chance of any person or material being affected by the 
current is small, or by arranging a bypath which 
shall carry the current safely away in case live parts 
of the conductors come in contact with it. To provide 
such a shunt is the object of all grounding. 

Wherever a ground connection is provided, it in¬ 
creases the liability of a breakdown in the insulation 
of the device, but at the same time reduces the possi¬ 
bility of serious damage from that source. Connect¬ 
ing the frame of any device to ground weakens the 
natural insulation of that device, but protects persons 
and property otherwise liable to injury to a consider¬ 
able extent. Good cause for the grounding of live 
parts of electrical circuits for the purpose of protec¬ 
tion exists only in cases where two or more voltages 
exist in such close proximity that there is liability of 
the higher voltage becoming impressed upon parts 
normally intended only for the lower voltage. And 
even under these conditions the N. E. C. authorizes 
the grounding only when, normally, no current is 
supposed to be flowing over the ground connections. 
The grounding of any part of a live circuit under the 
above conditions increases the chances of trouble but 
confines the trouble to that which may be possible 
with the lower voltage. If, for instance, the ground 
on the secondary of a transformer is in perfect con¬ 
dition, it will give positive assurance that the primary 
voltage cannot be impressed upon any part of the 
secondary system, but it will also give assurance that 


92 


ELECTRICAL TABLES AND DATA 


any workman who may come in contact with live 
parts on the ungrounded side, while making a ground 
himself, will receive the full benefit of the secondary 
voltage. In general, since the grounding takes away 
the natural insulation, which is often relied upon to 
some extent but quite often does not exist at all, it 
will force upon manufacturers a higher standard of 
construction, and the net result will be increased 
safety in all respects except life. In order to keep 
the life hazard within bounds it is not customary to 
ground live wires operating with a potential above 
250. 

As a general rule, all metallic structures or pipes 
not normally connected to electrical sources, but 
liable to be accidentally so connected, should be 
grounded. Connection to an extensive water pipe 
system makes the best possible ground. Steam and 
hot water piping is not so reliable even if connected 
to water pipe systems. The steel frames of buildings 
are useful only with supposedly small currents con¬ 
fined to the same building. Gas piping is likely to 
cause fires if contacts work loose, or if there is any 
electrolytic action. Where the above means of making 
ground connections are not available the most eco¬ 
nomical connection is made with a galvanized iron 
pipe driven into the ground. The practice of one 
large company is to use a l-|-inch pipe 8 feet long, 
and drive its full length into the ground, burying the 
connection with it. Another company uses a -J- or 
f-inch pipe. The resistance of the ground itself is 
so much higher than that of the pipe that the con¬ 
ductivity of the larger pipe is not much better than 
that of the smaller, but it is more reliable for driving 
purposes. Where the ground is of very great impor¬ 
tance, it is advisable to use several pipes. The pipe 
should enter the earth at least 6 feet, and it is prob¬ 
able that an additional foot or two will more than 


ELECTRICAL TABLES AMD DATA 


03 


double the usefulness in dry seasons. The resistance 
of the earth varies with its composition, its degree of 
moisture, and distance from piping, etc. Gravel and 
sand, because so easily drained, make very poor 
grounds, and rock cannot be used at all. 

Overhead cables and messenger wires are provided 
with about one ground per mile. Ground connections 
may be tested with an ammeter and a voltmeter. 

Connect one pole of current source to nearest hy¬ 
drant or other available piping and the other to the 
ground. The voltage divided by the current will 
equal the resistance of the ground, since the piping 
itself may be considered as comparatively without 
resistance. 

Hanger Boards are required for incandescent 
lamps indoors on series circuits, but are not neces¬ 
sary with arc lamps, although advisable. 

Heat Coils are usually installed in connection with 
signaling circuits. They are arranged to open the 
circuit when a large current flows through them for 
a short time or a small current for a longer time. 
Their office is to guard against sneak currents too 
small to blow fuses. 

Heating by Electricity. —The heating of buildings 
by electricity is not commercially practicable, except 
on a small scale, or under particularly favorable cir- 
sumstances. It is used on a large scale only in con¬ 
nection with street cars. In residences, offices, fac¬ 
tories, etc., it is used only for small spaces, or where 
a limited quantity of heat is required for a short 
time only. Since there is practically no heat wasted, 
no air vitiated, little space occupied, no dirt caused, 
the fire hazard greatly reduced and the heaters are 
easily portable, it compares under suitable conditions, 
very favorably with other means of heating. One 
watt hour will raise the temperature of 1 cubic foot 
of air about 200 degrees Fahrenheit. 


94 


ELECTRICAL TABLES AND DATA 


The heat represented by one B. T. U. is sufficient to 
raise the temperature of 1 lb. of water or 55 cubic 
feet of air 1 degree Fahrenheit. One watt equals 
3.412 B. T. TJ.s. 

In order to heat a room properly we must first 
supply sufficient heat to raise the temperature the 
required amount; next, furnish a steady supply of 
heat to make up for the absorption of walls, floor and 
ceiling; third, heat the fresh air which must be ad¬ 
mitted for ventilating purposes. For a rough esti¬ 
mate it is customary to require from one to two 
watts per cu. ft. in room. 

The wattage necessary to raise the temperature of 
a room may, however, be more accurately found by 
the formula: 

£x# 60 

W ~ 200 to 

where W = watts 

(7 = cubic feet of air in room 
t = number of degrees F. that temperature 
must be raised 

m=the number of minutes in which this rise 
must take place. 

The above formula makes no allowance for radiation 
or ventilation. 

Under average conditions it may be assumed that 
every square foot of wall, ceiling, and floor space will 
absorb heat as given in Table XXX for various tem¬ 
peratures. If we multiply the surfaces by the num¬ 
bers given we shall obtain the rate at which watts 
must be supplied to maintain the temperature in a 
hermetically sealed room after the desired tempera¬ 
ture has been secured. 

Every human being should be provided with 3,000 
cubic feet of fresh air per hour, although it is possible 



ELECTRICAL TABLES AND DATA 


95 


to do comfortably with 2,000 feet. If the allowance 
per hour, however, is as low as 1,000 feet, conditions 
will be decidedly injurious to health and also imme¬ 
diately uncomfortable. Since all rooms electrically 
heated are small, fresh air requirements demand that 
the air must be changed several times per hour. In 
order to facilitate the calculations three tables are 
provided. Table XXVIII shows the number of cubic 
feet of air contained in rooms of various dimensions 
likely to be warmed with electrical heat, the height of 
rooms being assumed as 9 feet. This table also shows 
the number of square feet of radiating surface, includ¬ 
ing ceiling and floor. There is further given, in 
connection with each size of room, the number of times 
the air should be changed per hour for each occupant 
to afford fair ventilation. The figures given are such 
as it is believed the occupants will naturally provide 
by opening windows or doors. 

In Table XXIX we have constants by which the 
cubic contents of rooms must be multiplied to find 
the number of watts necessary to raise the tempera¬ 
ture of rooms the number of degrees given at top, in 
the number of minutes given at the left. To find the 
watts necessary to provide for air changes per hour 
we must multiply the cubic contents by the constants 
given for 60 minutes and by the number of times per 
hour the air is to be changed. 

To find the watts lost in radiation we multiply the 
wall surface by the figures given in Table XXX. 

Example .—A bathroom 6 by 8 feet is to be heated 
20 degrees F. above the temperature of the surround¬ 
ing rooms and the rise in temperature must be brought 
about in five minutes and then maintained for an 
hour afterward. What size of heater will be required ? 
There are 432 cu. ft. in such a room and by Table 
XXIX for 20 degrees and five minutes we find 1.20 
and multiplying this by 432 we have 518 watts re* 


96 


ELECTRICAL TABLES AND DATA 


quired to heat the air without allowing for conduction 
or ventilation. From Table XXVIII we also see 
that there are 348 feet of surface which, multiplied 
by 2.5, taken from Table XXX, for twenty degrees, 
give us 870 watts to make up for conduction through 
walls. Table XXVIII further shows that the air 
ought to be changed five times per hour; hence, tak¬ 
ing the constant 0.10 from Table XXIX for 60 min¬ 
utes and 20 degrees and multiplying this by 5, we 
have 0.50, and this, multiplied by the number of 
cu. ft., gives us 216 watts for air changes, and this, 
added to 870 watts for conduction, gives us a total 
of 1,088 watts to keep up the temperature of four 
bathroom 20 degrees above that of the surrounding 
rooms. A 1,500-watt heater would serve such a room 
very nicely. 

Every occupant of such a room will contribute 
about 125 watts of this. 

With all doors and windows closed the average 
house is supposed to allow a change of air at least 
once per hour. 

If a room is to be used only for a short time, a 
change of once per hour may thus be calculated upon. 
In laying out heating plants in residences where com¬ 
fort of the user is the main desideratum, it is advis¬ 
able to err on the side of plentiful capacity; in com¬ 
mercial installations where the installation is more 
for the benefit of workmen it may be more judicious 
to err in the interest of a somewhat small capacity. 

In small rooms a heater should always be placed 
as near as possible where the cold air enters, but in 
large rooms, if only a portion of the room is to be 
heated, it should be located out of the way of drafts. 
The coils should be divided into proportional sections 
equal to 1 and 2. This will enable l/3d, 2/3ds or 
the full capacity of the heater to be used as desired. 
Electric heating has one advantage over other forms. 


ELECTRICAL TABLES AND DATA 


97 


and this consists in its ability to give instantaneous 
results, and these are best attained with heaters of 
comparatively large capacity, so that there will be no 
temptation to keep up the temperature except when 
it is actually needed. 


TABLE XXVIII 

Showing number of cu. ft.; wall surfaces (includ¬ 
ing ceiling and floor) and necessary changes of air per 
occupant per hour in room of dimensions given; height 
of ceiling 9 ft. 


Width Length in Feet. 




5 

6 

7 

8 

9 

10 

11 

12 


rcu. 

feet.225 

270 

315 

360 

405 

450 

495 

540 

5 

Wall surface. .230 

258 

286 

314 

342 

370 

398 

426 


[Air 

changes.. 9 

8 

7 

6 

5 

5 

4 

4 


'Cu. 

feet.270 

324 

378 

432 

486 

540 

594 

648 

6 

Wall surf ace.. 258 

288 

318 

348 

378 

408 

438 

468 


Air 

changes.. 8 

6 

6 

5 

4 

4 

4 

3 


rcu. 

feet.315 

378 

441 

504 

567 

630 

693 

756 

7 1 

Wall surface..286 

318 

350 

382 

414 

446 

478 

510 


Air 

changes.. 7 

6 

5 

4 

4 

3 

3 

3 

• 

'Cu. 

feet.360 

432 

504 

576 

648 

720 

792 

864 

8 

Wall surface..314 

348 

382 

416 

450 

484 

518 

552 

1 

Air 

changes.. 6 

5 

4 

4 

3 

3 

3 

3 


rcu. 

feet.405 

486 

567 

648 

729 

810 

891 

972 

9 1 

Yfall surf ace.. 342 

378 

414 

450 

486 

522 

558 

594 


[Air 

changes.. 5 

4 

4 

3 

3 

2.5 

2.2 

2 


rcu. 

feet.450 

540 

630 

720 

810 

900 

990 

1,080 

1° J 

Wall surface..370 

408 

446 

484 

522 

560 

598 

636 

I 

Air 

changes.. 4.4 

4 

3.2 

3 

2.5 

2.3 

2 

2 


"Cu. 

feet.495 

594 

693 

792 

891 

990 1,089 1,188 

11 \ 

Wall surface..398 

438 

478 

518 

558 

598 

638 

678 


Air 

changes.. 4 

3.2 

3 

2.6 

2.2 

2.0 

1.9 

1.7 


'Cu. 

feet.540 

648 

756 

864 

972 1,080 1,188 1,296 

12 J 

Wall surface..426 

468 

510 

552 

594 

636 

678 

720 

1 

Air 

changes.. 4 

3 

2.6 

2.3 

2 

2 

1.8 

1.7 














98 


ELECTRICAL TABLES AND DATA 


TABLE XXIX 


To find watts required to heat air in room (no 
allowance for radiation or changes) multiply cubic 
feet of air by factor in table below. 


Minutes in which 


Eise 

in Temperature, 

F. 


rise is to take place 

10 

15 

20 

25 

30 

35 

40 

5 

0.60 

0.90 

1.20 

1.50 

1.80 

2.10 

2.40 

10 

0.30 

0.45 

0.60 

0.75 

0.90 

1.05 

1.20 

15 

0.20 

0.30 

0.40 

0.50 

0.60 

0.70 

0.80 

30 

0.10 

0.15 

0.20 

0.25 

0.30 

0.35 

0.40 

45 

0.07 

0.10 

0.14 

0.17 

0.20 

0.23 

0.27 

60 

0.05 

0.07 

0.10 

0.12 

0.15 

0.18 

0.20 


TABLE XXX 

To find watts needed to make up for conduction 
multiply wall surface by factors below. 

Temperature Eise 

10 15 20 25 30 35 40 

1.5 2.0 2.5 3.1 3.6 4.3 5.0 

To find watts necessary for ventilation, multiply 
watts required to heat air in 60 minutes by number 
of changes of air required per hour. 


DOMESTIC HEATING DEVICES 
(Westingliouse Electric & Mfg. Co.) 


Apparatus Watts 

Broilers, 3 lit. 300 to 1,200 

Chafing dishes, 3 ht. 200 to 500 

Cigar lighters. 75 

Coffee percolators. 380 

Coil heaters. 110 to 440 

Corn poppers. 300 

Curling irons. 15 

Curling iron heaters. 60 










ELECTRICAL TABLES AND DATA 


99 


Apparatus Watts 

Double boilers for 6 in. 3 ht. stove. 100 to 440 

Flat irons, 3 to 8 lbs., domestic sizes. 250 to 635 

Foot warmers. 50 to 400 

Frying kettle, 8 in. 825 

Frying pan. 250 to 500 

Griddle cake cookers, 9x12, 3 ht. 330 to 880 

Griddle cake cookers, 12x18, 3 ht. 500 to 1,500 

Grill. 600 

Heating pads. 50 

Instantaneous flow water heaters.2,000 

Kitchenettes (complete), average.1,500 

Nursery milk warmers. 500 

Ornamental stoves. 250 to 500 

Ovens .1,200 to 1,500 

Plate warmers. 300 

Radiators . 500 to 6,000 

Ranges, three heats, 4 to 6 people.1,000 to 4,515 

Ranges, three heats, 6 to 12 people.1,100 to 5,250 

Ranges, three heats, 12 to 20 people.2,000 to 7,200 

8amovar . 500 

Saute pans. 165 to 660 

Shaving mugs. 150 

Stoves (plain) 4 in. 50 to 220 

Stoves (plain) 6 in., 3 ht. 125 to 500 

Stoves (plain) 7 in., 3 ht. 120 to 600 

Stoves (plain) 8 in., 3 ht. 165 to 825 

Stoves (plain) 10 in., 3 ht. 275 to 1,100 

Stoves (plain) 12 in., 3 ht. 325 to 1,300 

Stoves, traveler’s. 200 

Toaster stoves, 5 in. by 9 in..... 500 

Toasters, 9 in. by 12 in., 3 ht. 330 to 880 

Toasters, 12 in. by 18 in., 3 ht. 500 to 1,500 

Urns, 1 gal., 3 ht. 110 to 440 

Urns, 3 gal., 3 ht. 220 to 440 

Urns, 3 gal., 3 ht. 330 to 1,320 

Urns, 5 gal., 3 ht. 400 to 1,700 

Waffle irons, two waffles. 770 

Waffle irons, three waffles.1,150 

Water cup. * . 500 

Water heater, bayonet type. 700 to 1,500 










































100 


ELECTRICAL TABLES AND DATA 


ELECTRIC HEATING DEVICES FOR INDUSTRIAL PURPOSES 

Apparatus Watts 

Annealing furnaces. 200 

Bar or barbers’ urns, 1 to 5 gal., 3 ht. 200 to 1,700 

Bakers’ ovens, 30 to 80 loaves. 6,000 to 10,000 

Branding tool. 10 to 500 

Button dye heater. 100 

Chocolate warmers. 55 to 250 

Coffee urns, 1 to 20 gal. 200 to 4,000 

Corset irons. 350 

Dental furnaces. 450 

Embossing head .. 100 to 1,000 

Glue pot, pt. to 25 gal. 150 to 5,000 

Glue pots. 110 to 880 

Hat irons (small). 200 

Hatters’ iron, 9 to 15 pounds. 450 

Instrument sterilizers. 350 to 500 

Japanning oven. 1,000 to 10,000 

Laboratory apparatus flask heaters. 500 

Linotype pots. 485 

Machine irons, 2 to 18 lbs. 770 

Matrix dryer.28,000 

Melting pot.13,000 to 30,000 

Oil tempering bath. 6,000 to 20,000 

Pitch kettles, 12 and 15 iu. 3 ht. .. 300 to 1,500 

Polishing irons, 3.5 to 5.5 lbs. 330 to 550 

Radiators, various sizes. 700 to 6,000 

Sealing wax pots, .5 to 1.5 pt. 175 to 300 

Shoe irons. 200 

Soldering irons (various sizes). 100 to 450 

Soldering pots, 4 to 15 lbs. capacity. 200 to 440 

Tailors’ iron, 12 to 25 lbs. 660 to 880 

Yulcanizers for automobile tires. 100 to 450 


































ELECTRICAL TABLES AND DATA 


101 


High Tension.—The N.E. C. classifies as “high 
potential” all voltages above 550 and below 3500, 
allowing a 10 per cent additional in the case of 550 
volt motors. Voltages above 3500 are classed as 
“extra high potential.” Special points to be noted 
with very high potentials are the Corona effect and 
the fact that ordinary bushings must not be used 
where wires enter buildings. It is best to enter wires 
through large open spaces. 

Horsepower. —74’6 watts equal 1 horsepower, 
abbreviated H. P. One H. P. is sufficient to raise 
33,000 lbs. 1 foot per minute or 1 lb. 33,000 feet per 
minute. 

Hospitals.— In the corridors, only an indifferent 
illumination of about 0.5 watts per square foot is 
needed. Good exit and emergency lighting is usually 
insisted upon and as most of the inmates are helpless 
every possible precaution against the fire hazard 
should be taken. Good ventilation is also essential. 

In the public wards inverted lighting or lights 
encased in strongly diffusing globes would give the 
best results. By no means should direct lighting 
from the ceiling be favored. A plentiful supply of 
outlets for heating pads, etc., will be found convenient. 

In the private wards the illumination should be by 
means of lights placed at the head of bed and never 
by ceiling lights. Each lamp should be controllable 
by pendant switch, so as to enable patient to operate 
it. Separate receptacle for heating pads and other 
devices should be provided. In the operating rooms a 
very bright shadowless illumination should be pro¬ 
vided, and this should be fitted with ample switching 
facilities so as to adjust it to the special needs of any 
operating physician. Arrange the operating lights so 
that no one fuse can put all of them out, or at least 
provide throw over switch to another set of fuses. 
Signaling circuits are usually also provided for all 
patients. 


102 


ELECTRICAL TABLES AND DATA 


Hotels.—Exit and emergency lights should be pro¬ 
vided in all large hotels. It is a good plan to arrange 
the lighting so that two circuits enter each room or 
apartment which contains more than one outlet. 
Where floors are alike this can sometimes be done by 
running branch circuits straight up and down, and 
locating all cut-outs in basement. Hall circuits should 
always be independent of room circuits, so as to reas¬ 
sure guests in case of a blowout of large fuse, or other 
accident which darkens a large part of the house. 
Door switches will be found useful for closets as well 
as for rooms. Vacuum cleaner circuits should be pro¬ 
vided in all halls, close enough together to avoid the 
use of very long cords. In the case of hotels planned 
for families, a large number of outlets with which to 
supply lights for illumination of pictures, lamps in 
cozy corners, etc., will be useful. If these are not pro¬ 
vided, the rooms will likely soon be found strung full 
of flexible cord, which will introduce a considerable 
fire risk. Special systems of wiring enabling one to 
turn on lights in rooms even though they be switched 
off there, will be very serviceable in case of fire or 
panic, but will add considerable to the expense. In 
large hotels equipped with banquet halls, carriage 
calls are often provided. In such halls a special outlet 
for moving picture arc, or stereopticon should be 
provided. 

Hunting.—Whenever anything causes fluctuations 
in the speed of an alternator operating in parallel with 
others, it will either deliver current to the others or 
draw current from them. Under certain circumstances 
this condition may become fixed and the machines are 
then said to be hunting or phase swinging. This 
condition is liable to be most severe with machines 
having a large number of poles. To prevent hunting 
the prime mover should have a governor which is not 
too sensitive. The connections between the machines 


ELECTRICAL TABLES AND DATA 


103 


should not have too much resistance, and the ma¬ 
chines should be equipped with damping coils. To 
prevent excessive short circuits, reactances are some¬ 
times cut into the external circuit. To prevent over¬ 
heating, thermometers or pyrometers electrically con¬ 
nected are sometimes embedded in the hottest parts 
of machines and arranged to indicate temperatures 
at the outside. 

Hysterisis. —This is the term which describes the 
lagging of the magnetism behind the magnetizing 
force. It causes heating of the iron and loss of 
energy, and is much greater with steel than with soft 
iron. 

Illumination. —Illuminating engineering is more 
an art than a science, and to master it properly re¬ 
quires considerable experience and knowledge of many 
factors which can only be hinted at in a work of this 
kind. By means of the hints given out and the tables 
following, anyone, however, should be able to design 
a pretty satisfactory installation where ordinary com¬ 
mercial effects are desired. Where special effects in 
illumination of statuary, altars, etc., is desired, experi¬ 
ments with temporary lights should be made. The 
main requisite, where economy is not too much insisted 
upon, is plenty of capacity. It is never advisable to 
figure illumination for light colors, since colors are 
apt to be changed. If there is plenty of circuit ca¬ 
pacity, a wide choice as to candle power of lamps 
possible and many experiments may be made until the 
most satisfactory effects are obtained. In addition to 
the matter contained in this chapter, practical hints 
on the illumination of special places are given in the 
alphabetical order of locations referred to, and it is 
advisable to consult these before deciding upon any 
work. 

The circuit capacity necessary to be installed to 
arrange for any degree of illumination can be deter- 


104 


ELECTRICAL TABLES AND DATA 


mined readily by reference to Table XXXI. Multiply 
the floor area to be illuminated by the number of watts 
per square foot recommended with the various illumi- 
nants and by the foot candles desired. The result will 
give the number of watts for which provision should 
be made. Except in special cases (see National Elec¬ 
trical Code Rules ) one circuit at least should be pro¬ 
vided for each 660 watts. If large units are used, the 
first cost will be less, but evenness of illumination will 
be sacrificed unless lamps can be hung high. 

The intensity of illumination obtainable from a 
given source varies with the height and distribution 
of lamps; condition, type and kind of reflectors or 
enclosing globes; nature and color of ceilings and 
walls; also with the voltage maintained, and is never 
quite the same at all parts of the working plane. 

The figures given below are intended as approxima¬ 
tions and for quick determination of the number of 
lamps required. The watts per square foot given in 
connection with the various illuminants are thought 
to be sufficient to provide an illumination of one foot 
candle; for greater intensities they must be multiplied 
by the number of foot candles desired. 

Table XXXII is prepared to illustrate the difference 
in the quantity of wiring material required for illumi¬ 
nation brought about by the use of large and small 
units or clusters of lamps. The line “Wire used per 
sq. ft.” refers only to the wire (one leg) used between 
lamps. The wire needed to feed the circuits must be 
separately calculated. In case of arc lamps, or large 
incandescent lamps using one per circuit, no wire 
between lamps will be used. No allowance is made for 
switches or drops to brackets and it is assumed that 
circuits are run according to N. E. C. rules, never more 
than 660 watts per circuit. The table is not quite 
accurate unless the space illuminated is of such size as 
to allow of the use of full circuits. 


globes . 0.26 0.40 0.39 0.58 Bluish white 

Enclosed arc; multiple; opal in¬ 
ner and clear outer globes... 0.36 0.54 0.54 0.81 Long arcs may 

Enclosed arc; multiple; opal in- bluish white, or 

ner and outer globes. 0.42 0.63 0.63 0.95 into violet 


ELECTRICAL TABLES AND DATA 


106 


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TABLE XXXI—Continued 


106 


ELECTRICAL TABLES AND DATA 


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opal outer globe. 0.05 0.07 0.07 0.10 Yellow 

Regenerative flaming arc; mul¬ 
tiple; opal outer globe. 0.07 0.10 0.10 0.15 Yellow 











ELECTRICAL TABLES AND DATA 


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The table below shows the quantity of wire (one leg) required to connect 
between lamps for full circuits of lamps of wattages given; not more than 660 
watts on any circuit. 





















108 


ELECTRICAL TABLES AND DATA 


Average illumination, if made up of spots of very 
bright light alternating with low illumination, is no 
criterion of the value of illumination. The very bright 
spots only make the others appear less brilliant. The 
eye has great powers of adjustment and can get along 
with low illumination if it is even, but with elderly 
persons it cannot rapidly and often change its adjust¬ 
ment without causing pain and injury. The quantity 
of illumination should be adjustable, for not all per¬ 
sons can be comfortable with the same intensity. The 
source of light should never be visible, especially if it 
is of high intrinsic brilliancy. The best light is one 
sufficiently diffused to cast but a slight shadow. In 
offices, however, where one source of light must serve 
many persons, an absolutely shadowless inverted light 
is desirable. It is good practice to space outlets so 
that the space between lamps is from -one to two times 
the height of lamps above the working plane. This 
rule requires large units for high ceilings and small 
ones for low places. Special reflectors, however, have 
a certain ratio of spacing to height which should be 
obtained from the maker. Buildings containing many 
windows require more artificial light for night work 
than the ordinary building. i 

The following tables are based on Holophane 
Intensive, or medium reflectors, and will give fair 
approximations of results to be expected from other 
reflectors. Holophane reflectors are of high efficiency 
and in some cases allowance must be made for this. 

Incandescent Lamps. —These lamps are operated 
mostly in multiple, and when so used never at a higher 
voltage than 250. On series circuits the voltage used 
runs into the thousands, but special lamps are re¬ 
quired. Most lamps are built marked with three 
voltages: top, middle, and bottom. The top voltage is 
preferably used; with this voltage the efficiency is 
the highest but the life shortened; with botton voltage 


ELECTRICAL TABLES AND DATA 


Height of lumps in feet above plane to be illuminated. 

K>!olooi»-ilc5|oi|tfk| 


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tOMM 

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CO tO M 
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k^JOM 

Mrf*.b 

kt-tOM 

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ptcoto 

bbL 

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3.16 

6.53 

8.24 

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lamps 

4 Ft. 

to MO 
bbb 

COMM 

bbb 

rfk.tOM 

Mkfk.b 

kt*tOM 

<i<ib 

ptcoto 

bbL 

pcoto 

bbb 

CD OtCO 

bob 

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tween 

lamps 

»MO 

mcooc 

tOMM 

bbo 

COMM 

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COtOM 

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rf*-tOM 

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pcoto 
b L b 

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lamps 

CT 

to MO 
MCC00 

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bbo 

COtOM 

bob 

COtOM 

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itktOM 

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lamps 

MM O 
6c m *vj 

10 M O 

bbb 

tOMM 

bbo 

COMM 

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COtOM 

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k^-tOM 

bLb 

prfk.J0 

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Under 

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6 Ft. 

MM O 

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COMM 

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MOO 

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MMO 

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MOO 

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COMM 

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B 

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O 


CQ 


- TABLE XXXIII 

2 Table Showing Illumination in Foot Candles from 25, 40 and 60 Watt Mazda or 



























































































































































TABLE XXXIV 

Table Showing Illumination in Foot Candles from 25, 40 and 60 Watt Mazda or Tung¬ 
sten Lamps Arranged in Two Rows at Heights and Distances Apart as Given in 


no 


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electrical tables and data 


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4.1 

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10.8 

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18.3 

6.8 

9.1 

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12.9 

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6.7 

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10.8 

16.8 

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4.7 

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10.8 

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ELECTRICAL TABLES AND DATA 111 


Height of lamp in feet above plane to be 

wl©laol<j!©lcn 

illuminated. 

i 

M 


aie-to 

©OCT 

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5.2 

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6.8 

9.3 

15.6 

6.6 

10.6 

17.7 

7.6 

12.3 

20.3 

8.6 

14.3 

22.4 

Under 

lamps 

3 Ft. 

CD or CO 

©Lb 

4.0 

6.6 

10.9 

4.9 

7.9 

12.9 

5.6 

8.8 

14.6 

6.2 

9.8 

16.3 

7.1 

11.0 

18.0 

8.1 

12.6 

20.8 

Be¬ 

tween 

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o^to 

bLb 

ODOICO 

bbb 

CDpM 

bbb 

4.1 

6.5 

10.7 

4.5 

7.0 

11.7 

6.0 

7.8 

12.5 

5.4 

8.8 

13.4 

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L® L 

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TABLE XXXV 

Table Showing Illumination in Foot Candles from 25, 40 and 60 Watt Mazda or 































































































































































Table Showing Illumination in Foot 


112 electrical tables and data 


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9.0 

12.8 

4.9 

7.6 

12.4 

4.6 

7.1 

11.6 

4.4 

6.6 

10.8 

4.1 

6.5 

10.6 

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cd©© 

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Under 

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6.7 

9.2 

13.9 

6.4 

8.3 

13.1 

4.9 

7.6 

12.6 

4.5 

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11.7 

4.5 

6.7 

11.0 

t^©t> 

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14.2 

23.2 

8.4 

12.8 

20.9 

rH d 
rH i-i 

6.8 

10.9 

18.0 

6.2 

9.9 

16.3 

6.1 

8.3 

14.0 

4.2 

6.9 

11.6 

Under 

lamps 

9.2 

16.2 

23.6 

8.4 

13.3 

21.8 

7.5 

11.8 

19.6 

6 7 
10.6 
17.6 

6.4 

9.8 

16.3 

4.9 

8.0 

13.4 

4.0 

6.4 

10.9 

. 

Wattage 

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ELECTRICAL TABLES AND DATA 


1 4 

Height of unit above plane illuminated. 

SlSIolml^loil 



Mwp 
Or Cl © 

ooo 

(Omm 

010*0 

OOO 

100 

150 

250 

100 

150 

250 

100 

150 

250 

100 

150 

250 

NM 

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Wattage 

05 CO tC 

bbb 

JO 

bbib 

CD pi CO 

bbb 

3.5 

6.2 

11 

1 -. -3 M 

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4.6 

8.0 

14 

5.4 

9.5 

16 

Under 

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05 CON 

bbb 

00^ JO 

obb 

CD pi CO 

bbb 

3.6 

6.3 

11 

4.0 

7.1 

12 

4.7 

8.2 

14 

6.3 

9.4 

16 

Be 

tween 

lamps 

OltOM 

Loo oo 

05 CO JO 

bbb 

-7M JO 

cobb 

OCvU JO 

bbb 

CDOlCO 

b*co b 

M CO 
^ tc b 

4.3 

7.5 

13 

Under 

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8 Ft. 

pi JOM 

bbb 

05 CO JO 
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bbb 

0 Drf».N 

bbb 

to pi CO 

bbb 

3.4 

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10 

3.7 

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11 

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bbb 

jom 

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pi CO JO 

bbb 

05 CO JO 

bbb 

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bbb 

cop! CO 

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8.8 

6.7 

12 

Under 

lamps 

10 Ft. 

^(OM 

bbb 

JOM 

boob 

Ol COM 

bbb 

05 CO JO 
Ol b M 

<7*. jo 

bbb 

JO 

bbb 

OCM JO 

bbb 

Be¬ 

tween 

lamps 

C0»M 
• • • 

*M60 

JOM 

obb 

pi com 

bob 

pi CO M 

bbb 

OJM 

bob 

bicca 

3.7 

6.4 

11 

Under 

lamps 

12 Ft. 

CO JOM 

bob 

►&.J0M 

©bob 

JOM 

bbb 

pi JO M 

obb 

pico- 

bbb 

pi COM 

bbb 

pi COM 

bbb 

Be¬ 

tween 

lamps 

COMM 

bbo 

CO JOM 

bbb 

M JOM 
05 05 01 

Ol COM 

bbb 

05 CO JO 
Olbb 

OOM JO 

bbb 

3.6 

6.2 

11 

Un¬ 

der 

l’mps 

14 Ft. 

CO M M 

bbb 

CO JO;-* 

bob 

1.3 

2.2 

3.8 

M JOM 

obb 

M JO m 

bbb 

3.4 

2.4 
4.1 

CO JOM 

bbb 

a * td 

05 3 

JO M © 

bbb 

COMM 

bbo 

^ JOM 

bbb 

Ol JOM 

bbb 

05 CO JO 

bbb 

OCrf^ JO 

bbib 

3.5 

6.0 

11 

Un¬ 

der 

l’mps 

10 Ft. 

»MO 

bbb 

COMM 

bbb 

COMM 

bbb 

COMM 

bbb 

COMM 

bbb 

COMM 

obb 

JOM© 

bbib 

Be- 

tw’en 

l’mps 

J5 MO 

bbb 

COMM 

bb'o 

•e- jom 

bbb 

OtNM 

bbb 

05 CO JO 

bbio 

JO 

bbib 

3.5 

6.0 

10 

Un¬ 

der 

l’mps 

18 Ft. 

JO M © 

bbb 

tO M © 

bbioo 

JOM© 

bbb 

JO MO 

bbb 

JO MO 

bibb 

JOM© 

bbb 

MM© 

bob 

Be- 

tw’en 

l’mps 

JO—© 

Ci3C0<l 

JO MO 
cobb 

1.3 

2.3 
4.0 

f- JOM 

bbb 

05 CO JO 

obb 

JO 

bbb 

3.4 

6.0 

10 

Un¬ 

der 

l’mps 

20 Ft. 

0.7 

1.1 

2.0 

JO M © 

Mbb 

NMO 

bbb 

MMO 

bbb 

0.6 

3.0 

1.8 

MOO 

bbb 

MOO 

bbb 

m o 9 

GD P 


o 

t—I 

W 

►3 

> 

3 


•v 

b 

w 

H 

o 

*1 

> 

% 

Ul 

k-H 

2 

H 

H 

^3 


113 


TABLE XXXVTT 

Table Showing Illumination in Foot Canddles from 100, 150 and 250 Watts Mazda 
Lamps Arranged in One Row at Heights and Distances Apart Given in Table. 
Bowl Frosted Lamps Equipped with Holophane Intensive Clear High Effi¬ 
ciency Reflectors Nos. 106,180, 106.185 and 106,190 Respectively. 


































































































































































TABLE XXXVIII 

Table Showing Illumination in Foot Canddles from 100, 150 and 250 Watts Mazda 
Lamps Arranged in Two Rows at Heights and Distances Apart Given in Table. 
Bowl Frosted Lamps Equipped with Holophane Intensive Clear High Effi¬ 
ciency Reflectors Nos. 106,180, 106,185, and 106,190 Respectively. 


114 


electrical tables and data 


c h 
cw 

% 

a 

o 

Eh 

9 

Oh 

a 

o 

fc 

EH 

m 

t-H 

Q 


20 Ft. 

Be- 

tw’en 

l’mps 

0.30 

0.60 

0.84 

0.36 

0.62 

1.04 

0.39 

0.70 

1.20 

0.43 

0.82 

1.40 

0.52 

0.90 

1.56 

0.60 

1.06 

1.84 

0.74 

1.14 

1.96 

Un¬ 

der 

l’mps 

3.49 

6.03 

10.6 

2.63 

4.51 

7.82 

2.04 

8.63 

6.10 

1.63 

2.84 

4.92 

1.39 

2.37 

4.11 

1.01 

1.78 

3.07 

0.87 

1.45 

2.48 

18 Ft. 

C ® 

© ® 2* 
mV a 

-*-3 0-4 

0.34 

0.68 

1.16 

0.43 

0.77 

1.40 

0.47 

0.94 

1.66 

0.55 

1.06 

1.87 

0.64 

1.19 

2.09 

0.76 

1.33 

2.36 

0.82 

1.43 

2.47 

Un¬ 

der 

l’mps 

3.62 

6.10 

10.7 

2.66 

4.59 

8.07 

2.07 

8.62 

6.40 

1.65 

2.95 

6.27 

1.42 

2.49 

4.50 

1.10 

1.92 

3.55 

0.93 

1.64 

3.05 

16 Ft. 

C 0D 
© ® 2* 
«V.B 

+3 0-4 

0.60 

1.12 

1.98 

0.70 

1.34 

2.40 

0.86 

1.60 

2.80 

0.98 

1.76 

3.10 

1.08 

1.90 

3.34 

1.20 

2.02 

3.48 

1.20 

1.98 

3.46 

Un- 

der 

l’mps 

3.69 

6.20 

10.9 

2.72 

4.73 

8.30 

2.16 

3.77 

6.68 

1.77 

3.13 

5.69 

1.52 

2.71 

4.87 

1.20 

2.19 

4.01 

1.11 

1.90 

3.51 

14 Ft. 

. a £ 

®.® a 

0.76 

1.66 

2.80 

0.90 

1.88 

8.32 

1.10 

2.16 

3.84 

1.26 

2.36 

4.12 

1.40 

2.48 

4.36 

1.36 

2.66 

4.44 

1.32 

2.48 

4.32 

Un¬ 

der 

l’mps 

3.69 

6.36 

11.16 

2.84 

4.93 

8.57 

2.29 

4.01 

6.98 

1.89 

3.40 

5.95 

1.71 

2.99 

6.26 

1.40 

2.52 

4.43 

1.31 

2.2o 

3.93 

12 Ft. 

Be¬ 

tween 

lamps 

1.34 

2.64 

4.56 

1.66 

2.98 

6.24 

1.86 

8.24 

6.64 

1.94 

3.34 

6.80 

1.96 

3.36 

6.80 

1.82 

3.22 

6.52 

j 1.68 

2.96 

' 6.14 

Under 

lamps 

3.95 

6.74 

11.6 

3.10 

6.36 

9.28 

2.55 

4.62 

7.80 

2.17 

3.98 

6.85 

2.04 

3.62 

6.21 

1.82 

3 18 

5.39 

1.65 

2.92 

4.85 

10 Ft. 

Be¬ 

tween 

lamps 

2.46 

4.44 

7.94 

2.79 

4.89 

8.52 

2.96 

4.94 

9.04 

2.83 

4.86 

8.54 

2.72 

4.71 

8.26 

2.44 

4.29 

7.56 

2.14 

3.79 

6.82 

Under 

lamps 

4,19 

7.33 

12.9 

3.45 

6.09 

10.6 

8.00 

6.34 

9.4 

2.72 

4.85 

8.47 

2.62 

4.49 

7.88 

2.25 

4.00 

6.98 

2.11 

8.61 

6.30 

8 Ft. 

Be¬ 

tween 

lamps 

4.66 

8.18 

14.0 

4.04 

8.06 

13.7 

4.32 

7.72 

13.3 

4.06 

7.22 

12.5 

3.82 

6.76 

11.7 

8.26 

1 6.84 

10.2 

2.92 

6.12 

8.8 

Under 

lamps 

6.01 

8.81 

15.4 

4.45 

7.72 

13.7 

4.14 

7.03 

12.4 

3.77 

6.49 

11.5 

3.52 

6.05 

9.63 

3.16 

6.30 

9.35 

2.83 

4.67 

8.35 

6 Ft. 

Be¬ 

tween 

lamps 

7.88 

14.1 

24.2 

-£> 

HOIO) 

rH<M 

6.60 

11.6 

20.2 

6.00 

10.6 

18.3 

5.48 

9.6 

16.6 

4.62 

8.00 

13.8 

3.88 

6.68 

11.7 

Under 

lamps 

7.03 

12.6 

21.6 

6.53 

11.4 

19.6 

6.01 

10.5 

18.2 

6.46 

9.7 

16.8 

6.12 

9.00 

15.6 

4.46 

7.73 

13.5 

3.86 

6.76 

11.7 


Wattage 

100 

150 

250 

100 

150 

250 

100 

150 

250 

100 

150 

250 

100 

150 

250 

100 

150 

250 

100 

150 

250 

O | t> | X j 05 

•pejBUjmnnj einqd ui 

S 

sdnmi 

s 1 s 

fQ t 






























































































































































ELECTRICAL TABLES AND DATA 115 

the opposite will be the case. See Table XXXIX for 
approximate effects. 

The efficiency of all lamps decreases with use. In¬ 
candescent lamps will not give good results with fre¬ 
quencies lower than 40; for outdoor illumination they 
have, however, been used with 25 cycles. The fluctua¬ 
tions are less noticeable with heavy filaments. 

Circuit Limitations .—Not more than 660 watts are 
generally allowed on circuits, but where small fixture 
wire and fiber lined sockets and flexible cords are not 
used there is no serious objection to 1320 watts per 
circuit, or 32 lights instead of the usual 16. 

Frosting .—Lamps are frosted to reduce the intrinsic 
brilliancy and through it become less harmful to the 
eye. Ordinary frosting reduces the c. p. from 5 to 10 
per cent, but shortens the life from 25 to 50 per cent. 
Bowl frosting has no appreciable effect upon the life. 
The effect of coloring upon the life of the lamp is 
about the same as that of frosting. The effect upon 
the c. p. varies with the color and its density. Amber, 
opal and yellow absorb the least; blue, green and pur¬ 
ple the most; blue and red are the most used colors. 
Not much illumination can be expected from colored 
lamps. In some cases lamps are merely bowl colored. 
The efficiency of incandescent lamps increases with 
the voltage, but the length of life decreases. To a 
certain extent, therefore, what is gained on the one 
hand is lost on the other. 

Table XXXIX is prepared to facilitate the calcula¬ 
tions necessary to be made in order to determine the 
most economical voltage at which to operate lamps. 
In the column “K.W. wasted” we give the K. W. 
wasted by the use of the middle or bottom voltage 
during the length of life corresponding to top voltage, 
which is considered the standard. In the column 
headed “Saving in lamp renewals” we give the per 
centage of lamp renewals avoided by the use of lamps 


11G 


ELECTRICAL TABLES AND DATA 


at the lower voltages. In order to find the money value 
of the watts wasted by any lamp we must multiply the 
figure given in the table by the c. p. of the lamp and 
the rate per K. W. In order to find how much the 
same combination wdll save us in lamp renewals we 
must multiply the cost of lamp by the figure in the 
column on ‘ 1 Saving in lamp renewals. ’ ’ If our calcu¬ 
lation shows a net saving it will be more profitable to 
use the lower voltage, otherwise use the higher. Ex¬ 
ample : With energy at 5 cents per K. W. and 25 
watt tungsten lamps costing 20 cents each, is it more 
economical to use the middle voltage than the top volt¬ 
age? A 25 watt lamp gives 20 c. p. and the K. W. 
wasted at middle voltage is 0.050; we have therefore 
20x0.050x0.05, which equals 0.05, or 5 cents wasted 
during 1,000 hours. On the other hand, we save 
0.23x0.20, which equals 0.046. The saving in cost of 
lamp renewals does not quite offset the loss by the 
lower voltage, hence the higher voltage* is more 
economical. 

In many cases such a calculation has merely an 
academic value. As long as the parties using the light 
are satisfied with that obtainable from the use of 
the lower voltage there is no economy in using the 
higher. 

Smashing Point .—The useful life of a lamp is gen¬ 
erally considered to be over when its c. p. has dropped 
to 80 per cent of its original value. 

The following table is based on average values. 
The improvement in lamps is at times very rapid and 
in case great accuracy is required the manufacturers' 
guaranteed data should be obtained and used instead 
of values here given. 

Inductance. —This is that property of an electric 
circuit which causes a current in it to create lines of 
force and thus produce a counter e. m. f. proportional 
to the rate of change of that current. 


ELECTRICAL TABLES AND DATA 


117 


TABLE XXXIX 


Comparative cost of illumination and lamp re¬ 
newals. 


Name of 

Voltage 

Watts 

Hours of 

K.W. 

Saving 
in Lamp 

Lamp 

Rating 

Per C.P. 

Life 

Wasted 

Renewals 

Mazda or 

Top. 

I 90 

1,000 


• • • • 

Tungsten 

Middle .. 

... ' L27 

1,300 

0.050 

0.23 


Bottom.. 

... 1.33 

1,700 

0.110 

0.41 

Tungsten 

Top. 

Tn large units the type “C” or 

Gas Filled 

Middle .. 


' is fully twice as 


Bottom. . 

efficient as the common tungsten 


Top. 

lamp 

small 

but a 
. . . 1.84 

but in connection with 
units there is no saving, 
whiter light is obtained. 
800 . 

Tantulum 

Middle . . 

... 1.91 

1,075 

0.056 

0.26 


Bottom.. 

.. . 2.00 

1,350 

0.128 

0.41 

Gem or 

Top. 

. . . 2.50 

500 


• • • • 

Graphitized 

Middle . . 

. . . 2.65 

700 

0.075 

0.28 

Filament 

Bottom. . 

. . . 2.83 

1,000 

0.165 

0.50 


Less Than 50 

Top. 3.16 

Watts 

750 


• • • • 

Carbon 

Middle .. 

.. . 3.40 

1,100 

0.180 

0.68 


Bottom. . 

.. . 3.61 

1,600 

0.337 

0.47 


50 

Top. 

Watts and 

... 2.97 

Over. 

650 


• • • • 

Carbon 

Middle.. 

.. . 3.18 

925 

0.136 

0.30 


Bottom. . 

. . . 3.39 

1,425 

0.273 

0.54 

























table xxxx 

See pages 121-122. Wire tubes will taKe b. & S. 


t-18 


ELECTRICAL TABLES AND DATA 


•d 

o> 

•*-> C3 

°2 

o 

o 

10 

co 


©3 

o ~ 

to O 

go 


t3 

• rH 

P 2 

m 

'd 

®*a 

« 


p 2 


« 


GO d 

Wi 

« 


©■»*©© 
iH O 


rC 00 W O O 

«-i o 

o 
o 


qo co 


Tft CO <M 


o o 
o 
o 


o o 
o o 
o 
o 


'd- cj 

© P i 

cn 3 W 
© d n3 

lJ 

*33® 2 

o « 

OD 


ID CO rt 


o o o o o o o 
o O o o o o o 
o O o o o o o 
o 


CqoOTftCMOOoOOOOO 
r-1 OOlOOOlOOO 

O Tfl CO 05 04 lO O 

° r-1 ft <M 


>d 

• rH 

d 


o 

> 

§2 fi « 

© O 

cc 3 

GO g 

« 


O lO r-i 


O O 
O O 
O 
O 


00 CO o o o 
o o 
o o 
o 


€>I°H 1° 


vSO vJO vSO vS0 vSO 
®' -t«' ct' ®' oo^ 
W N K 'f 


s* ^ ^ # 

H H H N N N 


ja^auiutQ 


O' 
eo 


ci 

*CS 


CO 


H2 


to eoto 


«e «e •*» 

r' I * 1 f V I I 1 • 


H HHN(M(MCOCO 


ajquureiqo 

q^guaq ;sa§uoq; 




atquutuiqo ^ 

q;Su8»q ^sa^ioqg 


^5 ^ ^ ^ ^ 

H N N O) H N N 


Three sizes in split tubes are obtainable. The inside diameters are 2 %4, 2 Ye4 
nd 3 %4. Length is 3 inches. 


ELECTRICAL TABLES AND DATA 


119 


TABLE XXXXI 


Tables showing dimensions of porcelain insulators. 
See Fig. 7. 

Wire of 


No. 

Height 

Over all 
Diam. 

Diam. 
of Hole 

Approximately 
Same Diam. 
Groove as Groove 

0 

21 

3 

U 

1 

350,000 

1 

3 

21 

A 

i 

0000 

2 

o 

mJ 

2 

1 

1 

2 

3 

U 

2 

A 

A 

4 

3WG 

U 

2 

A 

i 

0000 

3* 

2 

2 

A 

A 

4 

4 

111 

U 

f 

f 

6 

41 

U 

11 

f 

A 

4 

51 

1* 

1 

1 

A 

8 

6 

1 

11 

A 

1 

10 

7 

1 

1 

1 

A 

4 

8 

11 

1 

1 

A 

8 

9 

H 

f 

A 

A 

12 

10 

li 

If 

f 

I 

6 

11 

11 

11 

1 

1 

2 

12 

11 

If 

A 

A 

1 

13 

i 

If 

1 

f 

00 

15 

1A 

li 

A 

1 

2 

20 

2 

2 

f 

f 

00 

21 

21 

2 

1 

A 

' 1 

22 

If 

21 

1 

A 

350,000 

23 

H 

H 

f 

1 

350,000 

24 

li 

U 

A 

f 

00 

25 

H 

21 

11 

1A 

400,000 

26 

2 

21 

f 

A 

1 

29 

2§ 

21 

1 

if 

450,000 

36 

u 

li 

1 

f 

0000 

39 

li 

21 

i 

If 

450,000 


Split knobs are made only for wires from 14 to 8. 


120 


ELECTRICAL TABLES AND DATA 



No. 0 


No. 1 



No. 3 WO 



NO. 3 


No. 3ft 



No. 4 Ho. 4Vi 



No. 6si 



No. 0 Ho. T No. 8 



No. 30 




Ho. 3 





No. 31 




■o. to 


No 23 


No. tf 


Mo. M 


No. It 


Figure 7.—Porcelain Insulators. 









ELECTRICAL TABLES AND DATA 


121 


TABLE XXXXII 


One Wire Cleats. 




• 


Smallest Size of 





Wire to Fill 

Height 




Out Groove 

Width 

Length Groove 

B.&S. 

U 

f 

2 

1 

8 

m 

f 

2 

ft 

8 

H 

1 

2f 

ft 

3 

2* 

1 

2* 

ft 

3 

If 

1* 

2 * 

1 

1 

2* 

1* 

2ft 

t 

1 

2f 

l$r 

2f 

i 

000 

2* 

1^ 

2f 

i 

000 

2| 

ltk 

3 

11 

250,000 

2i§ 

IfV 

3 

11 

250,000 

3f 

If 

3* 

lft 

6,000,000 

3f 

ItV 

311 

if 

750,000 

3f 

If 

4f 

2 

2,000,000 

4 

2 

5 

lft 

1,750,000 

4 

2 

5 

lft 

1,000,000 



Two Wire Cleats 




1 

3f 


14 



Three Wire Cleats 


lft 

f 

3» 

T$T 

14 


* The wire sizes given are thought to be the smallest the 
cleats will grip well. Diameters of wires, however, vary 
considerable and some single braid wires may be too small 
for the cleats with which they are supposed to go. See 
tables giving diameters of insulated wires. 


Insulating Materials. —The standard insulating 
materials are glass, porcelain, slate (without metal 
veins), marble, clay and certain compositions. The 
general requirement is that materials to be used for 


122 


ELECTRICAL TABLES AND DATA 


insulation shall be incombustible, shall not absorb 
moisture and shall not soften from heat. Wood and 
fiber are not approved, but are tolerated in some cases. 

The dimensions and other data concerning insu¬ 
lators, cleats and tubes are given in Tables XXXX 
to XXXXII. 

In buildings insulators must provide \ inch separa¬ 
tion between supports and wires and in damp places 
1 inch is required. 

Below are given sizes of bushings constructed ac¬ 
cording to the N. E. Code standard. Also the largest 
sizes of wire that can be used in them. The diameters 
of wires vary somewhat, and while it is believed that 
the wires given can be readily drawn through the 
bushings, it is advisable to use a larger bushing where 
it is necessary to draw wires through many of them, 
as in concealed knob and tube work. 

Logarithms. —Logarithms are used for multiplica¬ 
tion and division of large numbers, for raising num¬ 
bers to any power or extracting roots. Every log¬ 
arithm of the number 10 or greater than 10 consists 
of two parts—a whole number, which is known as the 
characteristic, and a decimal fraction known as the 
mantissa. The mantissa of all numbers consisting of 
the same digits is the same; thus in the table (which 
gives only the mantissa) we see that 0.8, 8, and 80 
each have the same mantissa, viz., .903 09, and this 
mantissa would still be the same for 800 or 8000. The 
characteristics of these numbers, however, are not the 
same, but always 1 less than the number of integers 
or whole numbers; thus for 8 it would be 0, for 80 it 
would be 1, making the logarithm of 8 = 0.903 09 and 
that of 80=1.903 09. If the number of which the 
logarithm is to be taken is less than unity, the charac¬ 
teristic is 1 greater than the number of ciphers which 
follow the decimal point. The characteristics of vari¬ 
ous numbers are given below. The characteristic of 


ELECTRICAL TABLES AND DATA 


123 


a number does not change unless that number be in¬ 
creased or decreased by one decimal place. 

1 000 000 = 6 
100 000 = 5 
10 000 = 4 
1 000 = 3 
100 = 2 
10 = 1 
1 = 0 
0.1 = 1 
0.01 = 2 
0.001 = 3 
0.0001 = 4 

The characteristics of logarithms of numbers less 
than 1 are treated as minus quantities and usually 
designated by drawing a line above them. 

The characteristics serve merely to determine the 
location of the decimal point. Whether they are added, 
subtracted or multiplied, if they are positive we must 
add to the number (found as hereafter described) 
ciphers enough so that the whole number will contain 
one more integer than the characteristic indicates. If 
the characteristic is minus, we must prefix one cipher 
less than the characteristic indicates. 

How to Find the Logarithm of a Number. —Trace 
along first column at the left until the first two digits 
of the desired number are found; next follow along 
the same horizontal line until the third digit is found. 
At this place the mantissa required will be found. 
Put this down, prefixing it w r ith a decimal point, and 
in front of it place a number equal to one less than 
the number of digits composing the original number. 
Example: find the logarithm of 676. Tracing down 
the left hand column, we come to the number 67 and 
in this horizontal line until we come to the third num¬ 
ber, 6, we find 829 95. As 676 contains 3 digits our 


124 ELECTRICAL TABLES AND DATA 

characteristic is 2 and we have 2.829 95, which is the 
logarithm of 676. 

How to Find a Number Corresponding to a Certain 
Logarithm. —This is accomplished by the reverse proc¬ 
ess. Suppose we wish to find the number whose log¬ 
arithm is 1.421 60; we first look for the mantissa part 
of it and find it in the horizontal line with 26 and 
under 4, giving us 264 as the required number; since 
the characteristic is 1 we locate our decimal point 2 
places from the left and the actual number now is 26.4. 

To Use Logarithms for Multiplication. —Find the 
logarithms of the two numbers; add them and find 
the number corresponding thereto. Example : What 
is the product of 36 x 88 ? 

log. 36 = 1.556 30 
log. 88 = 1.944 48 

3.500 78 

The mantissa nearest equal to 500 78 is 499 69, 
which corresponds to 316. Since our characteristic is 
3 we point off 4 from the left, giving us the number 
3160. 

To Divide by Logarithms. —Find the logarithms of 
the two numbers as before and subtract one from the 
other and find the number corresponding to the 
remainder. 

To Raise a Number to Any Power. —Find the log¬ 
arithm and multiply it by the index of the power. 
Example : What is the cube of 9 ? 

Log 9 = .954 24; this multiplied by 3 = 2.862 72; 
looking to the table we find 862 73 as the nearest and 
this corresponds to 729, and as our characteristic is 2 
we point off 3 from the left, which shows us that the 
desired number is 729. 

To Extract Roots. —Find the logarithm of the num¬ 
ber as before and divide by the index. Example: 
What is the cube root of 1331 ? The number 1331 is 



ELECTRICAL TABLES AND DATA 


125 


not tabulated, but the mantissa of 133 will be the 
same and it is 123 85 with a characteristic of 3, mak¬ 
ing it 3.123 85; this divided by 3 = 1.041 28, and the 
number corresponding to this is 11; since our char¬ 
acteristic is 1 we point off 2 from the left. 

The method of dealing with quantities less than 
unity is explained by the following example: What 
is the product of 0.079x0.87? The log of 0.079 is 
897 63 and as there is one cipher following the 
decimal point our characteristic is 2; the log of 0.87 
is 939 52 and as there is no cipher after the decimal 
point the characteristic is 1. We now add the man- 
tissae and the characteristics separately, and as the 
only characteristics are minus quantities, we subtract 
the positive characteristic found by adding the man- 
tissae from the sum of the negative characteristics 
with the net result as given below: 

2 .897 63 

1 .939 52 

3 1.837 15 

1 

2.837 15 


The nearest number in the tables to 837 15 is 
836 96 and this we see corresponds to the number 
688. As our characteristic is now 2 we prefix this 
number with one cipher, giving us 0.0688 as our 
product. 

In case the mantissa is not tabulated and the near¬ 
est one to it is not considered accurate enough, the 
approximate value of the corresponding number can 
be found by taking the numbers corresponding to the 
nearest two mantissae and noting their difference. 

Multiply this difference by —where a is the difference 

between the lowest mantissa and the one under con- 




126 


ELECTRICAL TABLES AND DATA 


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W CO N 00 05 


176 09 178 97 181 84 184 69 187 52 190 33 193 12 195 90 198 66 201 40 

204 12 206 83 209 52 212 18 214 84 217 48 220 10 222 71 225 30 227 88 

230 45 232 99 235 52 238 04 240 54 243 03 245 51 247 97 250 42 252 85 

255 27 257 67 260 07 262 45 264 81 267 17 269 51 271 84 274 15 276 46 

278 75 281 03 283 30 285 55 287 80 290 03 292 25 294 46 296 66 298 85 



CO CO CO CO CO 
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ELECTRICAL TABLES AND DATA 127 


CO CO CO CO CO 
4*WIOMO 

to to to to to 
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to to to to to 

4- CO to I—I > O 

No. 



Cl Cl Cl 4 4 
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p 

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CO co CO CO CO 
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w a oi o m 

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ci oo oo i—i co 

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Cl Cl Cl Cl 4* 
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m oo a to oo 

4 4 4 4 4 
a 4 to m 
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co co co co co 

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05 00 CO o o 

CO 



00 to M ^1 CO 

to o co co ci 

05 00 05 ^1 CO 

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4 CO 00 4 4 

CO CO co 4 4 






128 ELECTRICAL TABLES AND DATa 





ci i—i co co © 

b Cl H H Cl 

t-H b H H O 
00 t-H CO CO rH 

d b CO 05 b 
b H HI IO IO 

t-H t-H QO d CO 
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b b b b b 

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b b b b b 




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ELECTRICAL TABLES AND DATA 129 


-1 -1 ^1 -4 -1 
to GO N 05 Ol 

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4k WtOMO 

05 05 05 05 05 
tO OO S 05 Cl 

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No. 



OC 00 00 00 00 
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to 4* OD GO H 
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to CO G5 o co 

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M C5 O W 05 
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co to to 00 —4 
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Ol —4 -4 —4 05 
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O 

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to to M 00 H 
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co 


to 00 00 00 OO 
o to to OO s 

H Cl O 4*. to 

00 00 OO GO GO 

0 05 05 014k 

04 ^4 r-> Ol CO 

OO GO QO 00 GO 

4 k to to to M 

to C5 O 4k <t 

GO 00 — 4 —4 ^4 
h-i O tO tO GO 
O 4k -4 O 04 

—4 



4k. to 4- -i o 

Oi co to to 

CO 4k- Ol Ol 4k* 

CO 05 CO 4-k 4-1 

to to Ol 4-1 Ol 

CO 05 tO CO —4 

tO 4-i CO CO 4-» 
O 44 -4 tO tO 




to 00 GO 00 00 

O to to OO s 
toaoci to 

00 00 00 GO 00 
—4 05 05 Ol Ol 
(50 GO CO 05 O 

00 GO GO 00 00 

4k CO CO CO 1—1 

CO —4 1—1 4- 00 

OO GO — 4 —4 ^4 

1 —k O to to oo 

M 4k 41 O 03 

QO 



O Cl to to 05 

O CO GO 05 05 

tO O 4-i 4-i O 
OOlWCOW 

CO Ol CO —4 CO 

05 to CO 00 CO 

Ol 00 to to to 

00 CO 05 to o 




to 00 GO OO CO 
o to to co oo 

tOSMdO 

00 oo 00 00 00 
*1 05 05 Ol Ol 

4* 00 CO 05 O 

00 00 GO 00 CO 

4* CO W tO M 

4k- OO I—* Ol 00 

GO CO "“4 -4 ^4 

1—1 o to to 00 

CO Ol GO t—1 4k. 

to 



Ciottltoto 

4k —4 CO co 4*. 

4k 05 <| H 05 

QO 4- CO tO 4* 

4k CO 00 4k CO 

OO CO —1 co to 

CO Ol 05 C5 05 
4- O Ol tO CO 






130 ELECTRICAL TABLES AND DATA 


rtf 00 in CD o 

05 OJ 00 

O 

eo 

eo 

rH 

rH 

CO 

CO 

05 03 in fr- 05 

05 O 05 

05 

fr- 

IO 

CO 

O 

CO 

03 

C5 fr- CO 00 CO 00 

CO 05 CO 

00 

co 

00 

co 

00 

03 

fr. 

C> rH rH 03 03 

CO CO rtf 

rtf 

LQ 

in 

co 

co 

t- 

fr. 

05 05 05 05 05 

05 05 05 

05 

C5 

05 

05 

05 

05 

05 


rH IO CO H -1 05 

OO 03 05 

i—1 

fr. 

00 

rtf 

rtf 

o 

o 

N O (M CO 


rtf 

03 

O 

oo 

IO 

03 

oo 

00 fr- 03 00 CO 00 

co oo co 

00 

co 

CO 

03 

fr. 

03 

CO 

O H r- 1 03 03 

CO CO rtf 

rtf 

LO 

LO 

CO 

co 

fr. 

fr- 

05 05 05 05 05 

05 05 05 

05 

05 

05 

05 

05 

05 

05 


0 030C3M 

00 03 O 

03 

05 

O 

CO 

OO 

rtf 

LO 

CO 03 IO b- 00 

05 O O 

05 

fr- 

CO 

CO 

o 

fr. 

CO 

fr. CO 03 fr* 03 *>• 

03 00 CO 

fr- 

03 


03 

fc- 

rH1 

CO 

O rH H 03 03 

CO co rtf 

rtf 

LO 

IO 

CO 

CO 

fr 

fr 

05 05 05 05 05 

05 05 05 

05 

05 

05 

05 

05 

05 

05 





CO 05 00 H fr» 

fr rH O 

CO 

o 

03 

05 

rH 

fr- 

05 


OQ 


CO CO 05 03 CO 

rtf IO IO 

rtf 

co 

rH 

00 

CO 

03 

CO 

ft 

CO 

CO rH CO 03 fr» 

03 fr 03 

fr 

03 

fr 

rH 

CO 

rH 

IO 

“ 03 


O rH H 03 03 

COCOH 

rtf 

IO 

IO 

CO 

CO 

fr 

fr 



05 05 05 05 05 

05 05 05 

05 

05 

05 

05 

05 

05 

05 

a § 

• pH 











H- 

c 

i « 


a io in co w 

CO H O 

rtf 

03 

rtf 

03 

rtf 

rH 

CO 

fr" 

c 

> 


fr rH rtf CO 00 

05 o o 

05 

OO 

CO 

rtf 

rH 

00 

rtf 

c 

*£ 

LO 

W H CO H © 

rH fr* 03 

CO 

rH 

CO 

rH 

CO 

o 

IO 

1 

o 


O H H 03 03 

co co H 

rtf 

>o 

IO 

CO 

CO 

fr 

fr 

1 



05 05 05 05 05 

05 05 05 

05 

05 

05 

05 

05 

05 

05 

1— 

1 2 











1— 

s 












ra 


IO 03 03 CO rtf 

CO rH H 

IO 

CO 

co 

rtf 

fr¬ 

rtf 

fr 


• rH 


03 CO 05 rH CO 

IO IO 

rtf 

CO 

rH 

05 

ee 

CO 

05 


fn 

c3 

rtf 

•n o m h © 

rH CO rH 

CD 

rH 

CO 

O 

IO 

O 

rtf 


i hn 


O rH rH 03 03 

CO CO rtf 

rtf 

IO 

IO 

CO 

CO 

fr 

fr 


O 


05 05 05 05 05 

05 05 05 

05 

05 

05 

05 

05 

05 

05 















rH 05 O rtf 03 

in h h 

CO 

IO 

OO 

fr 

O 

GO 

rH 

3 


fr © rtf 00 

05 o o 

05 

oo 

CO 

rtf 

03 

00 

IO 

g 2 

CO 

rfioinoin 

O co rH 

IO 

o 

io 

O 

IO 

05 

rtf 

w s 


O H H 03 03 

CO CO rtf 

rtf 

io 

IO 

CO 

CO 

CO 

fr 

< 

g 


05 05 05 05 05 

05 05 05 

05 

05 

05 

05 

05 

05 

05 

E- 

• i 

r 














fr IO fr 03 rH 

rtf O rH 

CO 

co 

o 

05 

co 

rH 

in 




H in co H CO 

rtf in in 

rtf 

co 

03 

05 

fr 

rtf 

o 



03 

Ha^oin 

omo 

IO 

o 

‘O 

05 

rtf 

05 

rtf 




O O rH 03 03 

CO CO rtf 

rtf 

io 

IO 

IO 

CO 

CO 

fr 




05 05 05 05 05 

05 05 05 

05 

05 

05 

05 

05 

05 

05 


CO 03 rtf © 05 

CO O rH 

fr 

fr 

03 

rH 

CD 

m 

05 

eo o co co fr- 

05 O O 

05 

oo 

fr 

m 

03 

05 

m 

H CO 05 rtf 05 rtf 

05 in o 

rtf 

05 

rtf 

05 

rtf 

oo 

CO 

O O rH rH 03 

03 CO rtf 

rtf 

rtf 

m 

in 

CO 

CO 

fr 

05 05 05 05 05 

05 05 05 

05 

05 

05 

05 

05 

05 

05 



05 GO rH fr- fr- 

rH 05 rH 

GO 

05 

rtf 


00 

00 

03 


O rtf OO O 03 

rtf rtf in 

rtf 

CO 

03 

o 

fr. 

rtf 

r-H 

O 

CO 00 CO 05 rtf 

05 rtf 05 

rtf 

05 

rtf 

05 

CO 

00 

CO 


O O rH rH 03 

03 CO CO 

rtf 

rtf 

in 

m 

CO 

CO 

fr 


05 05 05 05 05 

05 05 05 

05 

05 

05 

05 

05 

05 

05 

No. 

O rH 03 CO rtf 

in CO fr- GO 05 

O rH 03 CO rtf 

GO 00 GO 00 00 

OO 00 GO 

00 00 

05 05 05 05 05 


95. 977 72 978 18 978 63 979 09 979 54 980 00 980 45 980 91 981 36 981 81 

96. 982 27 982 72 983 17 983 62 984 07 984 52 984 97 985 42 985 87 986 32 

97. 986 77 987 21 987 66 988 11 988 55 989 00 989 45 989 89 990 33 990 78 

98. 991 22 991 66 992 11 992 55 992 99 993 43 993 87 994 31 994 75 995 19 

99. 995 63 996 07 996 51 996 94 997 38 997 82 998 25 998 69 999 13 999 56 



ELECTRICAL TABLES AND DATA 


131 


sideration, and b the difference between the two man- 
tissae; next add this number to the lower number. 
Example: Our mantissa is 2.851 60, and looking into 
our table, we find that it is not tabulated. The next 
lower is .851 26, which corresponds to the number 700; 
the next higher is 2.851 87, which corresponds to 710. 
Now, .851 60- .851 26 leaves us 34, and the difference 
between 851 26 and 851 87 is 61. We have now 
34 

— x 10, which equals 5.57, and this added to 700 gives 

OJ 

us the approximate value of the number correspond¬ 
ing to the mantissa of 2.851 60, viz., 705.57. 

Magnetic Blowout. —A strong magnetic field repels 
an arc and is often used to break it. It is made use of 
in lightning arresters, and at other places where the 
arc is troublesome. 


TABLE XXXXIV 

Melting Points of Various Substances in Degrees Centigrade 




and 

Fahrenheit 




C. 

F. 


C. 

F. 

Aluminum .... 

. 659 

1218 

Mercury .. 

... .—38.7 

—37.7 

Antimony . . . . 

. 630 

1166 

Nickel .... 

....1452 

2645 

Bismuth . 

. 271 

'520 

Paraffin . . . 

_ 52 

126 

Brass . 

. 900 

1652 

Photo emulsion.. 32 

90 

Bronze . 

. 900 

1652 

Platinum .. 

....1755 

3191 

Carbon . 

.3600 

6512 

Rubber . ... 

.... 100 

212 

Chronium .... 

. 510 

950 

Silenium . . 

_ 218 

424 

Cobalt . 

.1490 

3714 

Silicon . . .. 

_1420 

2588 

German Silver.CL100 

2012 

Silver .... 

. 960 

1760 

Glass . 

.1300 

2372 

Steel, Av.. 

_1400 

2552 

Gold . 

.1063 

1945 

Sulphur . .. 

.... 110 

230 

Gutta Percha.. 

. 100 

212 

Tantalum . 

....2850 

5162 

Iridium . 

.2300 

4140 

Tin . 

. 232 

449 

Iron . 

.1520 

2768 

Tungsten . 

.3000 

5432 

Lead . 

. 327 

620 

Vanadium 

.1730 

3146 

Manganese ... 

.1225 

2237 

Wax, Bees. 

.... 62 

143 

Marble . 

.2500 

4532 

Zinc . 

.... 419 

787 


Bureau of Standards as authority for the majority. 

































132 


ELECTRICAL TABLES AND DATA 


Mains. —This term properly used applies only to 
the last set of wires feeding the final distribution point. 
Primary mains are those which feed the individual 
transformers. The wires leading from transformers 
are usually spoken of as secondary mains, although 



Figure 8.—Measurement of Heights and Distances. 


there may be conditions in which they would be sec¬ 
ondary feeders. 

Measurement of Heights and Distances. The 

measurement of heights and distances requires first 
of all the use of right angles. Where no instruments 
or squares are available, a right angle can be laid out 
as in G, Figure 8, setting stakes or stretching lines so 


















ELECTRICAL TABLES AND DATA 


133 


that the dimensions given, or multiples of them, obtain 
on the three sides. 

A square or rectangle can be proved by stretching 
diagonals from the corners. When both diagonals are 
the same length we have a perfect rectangle. See 77, 
Figure 8. 

The height of a pole or other object can be found 
by the method shown in 7, Figure 8. Set up two 
stakes, A and B, a known distance apart and of a 
height so that their tops form a straight line with top 
of pole. When this is done the length of pole C above 

T) Tp 

D is to E as D is to F, hence C=~^r- If the total length 

of D + F is made equal to 27J feet and F = 2$ feet, then 
C = 10xE. ’Add distance below line D to this to ob¬ 
tain total height of pole. 

The distance between two points, one of which is 
accessible, can be found by means of the construction 
shown in J, Figure 8. Similarly to the foregoing, 
if B is made 10 times C, then A will be made 10 
times D. 

The distance between two inaccessible points may 
be measured by the methods shown in K, Figure 8. 
If two stakes, C and 7), be set up with reference to 
A and B, so as to be at right angles to each other and 
with diagonals pointing to A and B, also forming the 
same angles, the distance between C and D will be 
equal to that between A and B. 

Another method consists in setting up two stakes, 
E and F, and parallel to them drawing a line or lay¬ 
ing a tape line upon the ground and setting up stakes 
as indicated at S. Measure distances between the 
various stakes and draw a plan of them to any con¬ 
venient scale as indicated. Measure the distance be¬ 
tween A and B on this plan. This method does not 
require that E and F be parallel or centered with 
reference to A and B. 



134 


ELECTRICAL TABLES AND DATA 


Mensuration- 

Area of a triangle = base x | altitude. 

Area of a parallelogram = base x altitude. 

Area of a trapezoid = altitude x^ the sum of parallel 
sides. 

Area of trapezium: divide into two triangles and 
find area of the triangles and add together. 

Area of circle = diameter 2 x 0.7854 = radius 2 x 3.1416. 

Area of sector of circle = length of arcx J the radius. 

Area of segment of circle = area of sector of equal 
radius-area of triangle, when the segment is less, 
and + area of triangle when the segment is greater 
than the semi-circle. 

Area of circular ring = diameters of the two circles x 
difference of diameters x 0.7854. 

Area of an ellipse = product of the two diameters x 
0.7854. 

Area of a parabola = base x § altitude. 

Area of regular polygon = sum of its sides x perpen¬ 
dicular from its center to one of its sides 2. 


REGULAR POLYGONS 


No. 


Area 
when 
dia. of 
inscribed 

Area 

when 

of 

Sides 

circle 

=1 

side 

=1 

3 

Triangle 

..1.299 

0.433 

4 

Square .. 

. .1.000 

1.000 

5 

Pentag. . 

. .0.908 

1.720 

6 

Hexag. .. 

. .0.866 

2.598 

7 

Heptag. . 

. .0.843 

3.634 

8 

Octag. .. 

. .0.828 

4.828 

9 

Nonag. .. 

. .0.819 

6.182 

10 

Decag. .. 

. .0.812 

7.694 

11 

Undecag. 

. .0.807 

9.366 

12 

Dodecag. 

. .0.804 

11.192 


Length 
Radius of 

Length of side when 


of circum- radius 

side Perpen- scribed of 


when 

dicular 

circle 

circum¬ 

perpen¬ 

when 

when 

scribed 

dicular 

side 

side 

circle 

=1 

=1 

=1 

=1 

3.464 

0.289 

0.577 

1.732 

2.000 

0.500 

0.707 

1.414 

1.453 

0.688 

0.851 

1.176 

1.155 

0.866 

1.000 

1.000 

0.963 

1.039 

1.152 

0.868 

0.828 

1.207 

1.307 

0.765 

0.728 

1.374 

1.462 

0.684 

0.650 

1.539 

1.618 

0.618 

0.587 

1.703 

1.775 

0.563 

0.536 

1.866 

1.932 

0.518 


ELECTRICAL TABLES AND DATA 


135 


Surface of cylinder or prism = area of both ends 4 - 
length x circumference. 

Surface of sphere = diameter x circumference. 

Convex surface of segment of sphere = height of seg¬ 
ment x circumference of the sphere of which it is a 
part. 

Surface of pyramid or cone = circumference of basex 
\ of the slant height 4-area of the base. 

Surface of frustrum of cone or pyramid = sum of cir¬ 
cumference at both ends x \ of slant height + area of 
both ends. 

Contents of sphere = cube of diameter x 0.5236. 

Contents of cylinder or prism = area of end x length. 

Contents of segment of sphere = (height 4- three times 
the square of radius of base) x (heightx0.5236). 

Contents of frustrum of cone or pyramid: Multiply 
areas of two ends together and extract square root. 
Add to this root the two areas x -J altitude. 

Contents of a wedge = area of base x | altitude. 

Circumference of circle = diameter x 3.1416. 

Circumference of circle = radius x 6.2832. 

Circumference of circle = 3.5446 x square root of area 
of circle. 

Circumference of circle x 0.159155 = radius. 

Circumference of circle x 0.31831 = diameter. 

Circumference of circle x 0.225 = side of inscribed 
square. 

Circumference of circle x 0.282 = side of an equal 
square. 

Half the circumference of circle x half its diameter = 
its area. 

Square of circumference of circle x 0.7958 = area. 

Diameter of circle x 0.86 = side of inscribed equilateral 
triangle. 

Diameter of circle x 0.7071 = side of an inscribed 
square. 

Diameter of circle x 0.8862 = side of an equal square. 


136 


ELECTRICAL TABLES AND DATA 


Diameter = 1.1283 Vsquare root of area of circle. 
Length of arc = number of degrees x 0.017453. 

Degrees in arc whose length equals radius, 57.2958°. 
Length of arc of 1° = radius x 0.017453. 

Meter Capacity. —It is a general rule to install 
meters of about one-half the capacity of the connected 
load in residences; three-fourths this capacity in small 
stores, offices, etc., and full capacity for elevator 
motor service and similar installations where exces¬ 
sive starting currents are the rule. For more exact 
determinations, see Demand Factors. 

The d. c. meter is essentially a shunt motor, and its 
direction of rotation is independent of the polarity, 
but if fed from the wrong side, it will run backwards. 
On a. c. circuits wattmeter readings will not check 
with volt and ammeter reading; the latter must be 
multiplied by the power factor. Current transform¬ 
ers are used in connection with large capacity a. c. 
meters. 

Meter Location. —Meters must always be accessi¬ 
ble, never in places that are locked or where meter 
readers would cause annoyance to occupants. The 
location selected must be free from moisture and 
vibration. Meters should not be placed on curb w T alls 
of streets on which cars operate nor on thin partitions. 
If meters are placed in cabinets, these should be fire¬ 
proofed and no magnetic material should be brought 
close to the meter. Meters must be set level and level¬ 
ing can be accomplished by placing a small weight 
upon disk, and shifting meter until disk remains at 
rest in any position. In order that meters may be 
properly set, meter boards must be provided. The 
necessary dimensions of such boards vary with the 
service to be rendered and are given on Figures 9 and 
10. These are the requirements in force in the City 
of Chicago. 


137 


ELECTRICAL TABLES AND DATA 


A D 



Figure 9.—Showing Proper Location of Meter Fittings and 
Size of Meter Boards Required for Different Installations. 

A. C. Residence or Apartment Lighting. 

30 sockets or 1500 watts, or under, sketch A. 

31 to 48 sockets or 1501 to 2640 watts, sketch B or D. 
Above 48 sockets or 2640 watts, sketch C or E. 

































































ELECTRICAL TABLES AND DATA 


luS 

A. C. Business Lighting. 

24 sockets or 1320 watts, or under, sketch A. 
Above 24 sockets or 1320 watts, sketch C or E. 
A. C. Power. 

5 H. P., and under, single-phase, sketch A. 
Above 5 H. P., and all three-phase, sketch C. 

Fr i 



Figure 10.—Meter Fittings and Meter Boards. 



































































ELECTRICAL TABLES AND DATA 139 

Figure 10.—Showing Proper Location of Meter Fittings and 
Size of Meter Boards Required for Different Installations. 

D. C. Residence or Apartment Lighting. 

30 sockets or 1500 watts, or under, sketch F. 

31 to 48 sockets or 1501-2640 watts, sketch G or I. 

Above 48 sockets or 2640 watts, sketch 77 or J. 

D. C. Business Lighting. 

24 sockets or 1320 watts, or under, sketch F. 

Above 24 sockets or 1320 watts, sketch 77 or J. 

D. C. Power. 

1500 watts, or under, sketch F. 

Above 1500 watts: 

2- wire, sketch G or 7. 

3- wire, sketch 77 or J. 

If the meter is located at service entrance, the meas 
ured energy will exceed the delivered energy by the 
percentage of loss occurring in the feed wires. If it 
is located at some distance from this point the service 
company will stand part or all of this loss. 

The per cent loss per 100 feet run with different 
voltages, wires assumed to be loaded to full capacity, 
is given in Table XXXXV. 


TABLE XXXXY 


B. & S. 

Amperes 

110 v. 

220 v. 

440 v. 

550 v. 

1000 v. 

14 

15 

4.80 

2.40 

1.20 

0.96 

0.53 

12 

20 

5.80 

2.90 

1.45 

1.16 

0.64 

10 

25 

4.50 

2.25 

1.13 

0.90 

0.50 

8 

35 

4.00 

2.00 

1.00 

0.80 

0.44 

6 

50 

3.60 

1.80 

0.90 

0.72 

0.40 

5 

55 

3.10 

1.55 

0.77 

0.62 

0.34 

4 

70 

3.10 

1.55 

0.77 

0.62 

0.34 

3 

80 

2.90 

1.45 

0.73 

0.58 

0.32 

2 

90 

2.60 

1.30 

0.65 

0.52 

0.29 

1 

100 

2.20 

1.10 

0.55 

0.44 

0.24 

0 

125 

2.20 

1.10 

0.55 

0.44 

0.24 

00 

150 

2.10 

1.05 

0.53 

0.42 

0.23 

000 

175 

1.90 

0.95 

0.47 

0.38 

0.21 

0000 

225 

1.90 

0.95 

0.47 

0.38 

0.21 

300 000 

275 

1.90 

0.95 

0.47 

0.38 

0.21 


140 


ELECTRICAL TABLES AND DATA 


Reactances are not taken into consideration. 

Meters, Maximum Demand. —The cost of supply¬ 
ing electrical energy is properly divided into two 
parts: One of these consists in charges to be made 
for meter reading, bookkeeping, and investment of 
capital; the other in the cost of energy consumed by 
the customer. 

The capital investment depends largely upon the 
maximum demand of the customer and also upon the 
time at which this demand occurs. A given trans¬ 
former, for instance, will serve perhaps twice as many 
families in which the ironing is done during the day, 
as it will where an iron is used at the same time with 
the lights. In order to obtain compensation for un¬ 
necessarily high demands for short times, maximum 
meters are installed, or a certain fixed charge per 
month is made against every customer whether cur¬ 
rent is used or not. 

The maximum demand meter may be any arrange¬ 
ment which will indicate the highest amperage, or 
rate of power consumption, during any month or 
other convenient term. The method of computing 
bills where these meters are installed is somewhat con¬ 
fusing to one who does not make a business of it, and 
to show the influence of max. meters the following 
table is presented: This table shows the average rate 
per K. W. hour brought about by different maximum 
demands and total K. W. consumption per month. 


TABLE XXXXVI 


Max. Amp. 

25 

50 

Total K.W. 
75 100 

Hours 

125 

150 

200 

300 

25 

11. 

11. 

11. 

10.1 

9.3 

8.7 

7.7 

6.4 

20 

11. 

11. 

10.4 

9.3 

8.6 

8.0 

7.0 

6.0 

15 

11. 

11. 

9.3 

8.4 

7.9 

6.9 

6.2 

5.5 

10 

11. 

9.3 

8. 

7. 

6.4 

6. 

5.5 

5. 

5 

9.3 

7. 

6. 

5.5 

5.2 

5. 

4.7 

4.4 


ELECTRICAL TABLES AND DATA 


141 


This table is based on a charge of 11 cents per K. W. 
hour for the first thirty hours of the maximum used; 
6 cents per K. W. hour for the next thirty hours of 
the maximum, and 4 cents per hour for the balance. 
The maximum load is found by multiplying the high¬ 
est amperage during the month by the volts. If we 
have a maximum of 10 amperes our first charge will 
be 10 x 110 x 30 x 0.11 = $3.63 ; the next will be 10 x 
110 x 30 x 0.06 = $1.98, and for the remaining K. W. 
hours we charge 4 cents, which equals $1.60, giving us 



a total of $7.21 for the 100 K. W. hours used, or ap¬ 
proximately 7 cents per K. W. In the table the change 
in rates per K. W. is shown as affected by the propor¬ 
tion between the maximum demand and the total 
consumption. 

Meter Reading. —This is a very simple matter 
when one has become accustomed to it, but is very 
confusing to those who have not had it to do. Most 
meters have five dials arranged somewhat on the order 
shown in Figure 11. These dials are all connected 
by gearing and serve merely as counters. The one at 
the right is driven by the meter mechanism proper, 
and through it the others are driven in turn. In the 






142 


ELECTRICAL TABLES AND DATA 


whole train each one revolves in a direction opposite 
to that of the one driving it, as indicated by arrows 
and also by the numbers used. The proportion of the 
gearing is such that while the pointer on the driving 
dial makes one complete revolution, the one on the 
next dial to the left makes only one-tenth of one 
revolution. From this it follows that any pointer, 
except the one at the extreme right, can be fully on 
any number only at the same time that the pointer to 
the right of it is on 0. This is the principal point to 
bear in mind in meter reading. In Figure 11 a com¬ 
plete revolution of any pointer indicates the use of 
the number of watt hours found at the top of that 
dial. Meter reading is best begun by noting the read¬ 
ing of the dials from right to left, although persons 
who have become accustomed to it find no trouble in 
reading from left to right. Let us begin reading our 
meter from right to left and note this rule: Put 
down the indication of the right-hand dial, and unless 
its pointer is fully on, or has just passed, 0, choose 
the lowest of the two numbers between which the 
pointer may be on the next dial, and continue in this 
manner, putting down each number to the left of the 
last. Following out this rule we have first 900, next 
8, then another 8, after that 1, and for the fifth dial 
another 1, giving us a total of 1 188 900 watt hours. 
Striking out 3 figures at the right reduces this to 
K. W. hours. It must be borne in mind that some 
meters are arranged to read directly in K.W. hours 
and some require the use of multipliers to determine 
the actual watts registered. 

Meter Testing.—In large cities meter fittings are 
usually provided for the connection of meters and 
the best of these are arranged to allow of easy con¬ 
nection for meter without interfering with the opera¬ 
tion of meters. On all meters the disk is arranged to 
make a certain number of revolutions per K. W. and 


ELECTRICAL TABLES AND DATA 


143 


if this is known the load on the meter at any moment 
can be determined. The relation between the num¬ 
ber of revolutions of the disk and the corresponding 
dial reading may be expressed by a multiplier which 
is known as the ‘‘constant” of the meter and is usually 
marked upon the disk or somewhere near it. The 
value of this constant in any particular instrument 
depends entirely upon the gearing between the disk 
and dial. Meter constants may be expressed in the 
following ways (1) number of watt hours indicated 
by one revolution of the disk; (2) the number of watt 
seconds indicated by one revolution of the disk; (3) 
the speed in R. P. M. at full load or rated load. 

If K stands for the constant of the meter in either 
of the meanings given above and R for the number 
of revolutions made in S seconds, the load passing 
through the meter during any interval of time will 
be found by the following formulae: 


1 . 

2 . 

3. 


Watts = 

Watts = 
Watts = 


KRx 3600 
8 
KR 
S 

KR 

8 


The testing of meters is best done by connecting a 
standard meter in series with it, and comparing the 
readings. The test meter may be connected so as to 
measure the operating current in addition to the load 
of the one under test. In this case the meter under 
test will be found “slow” if it is arranged to measure 
that current; if the test meter is connected to avoid 
this current the other will be found “fast.” Before 
making any test the meters should be allowed to be in 
circuit for about 15 minutes. A stop watch must be 
used if accurate results are required. On important 





144 


ELECTRICAL TABLES AND DATA 


installations it is advisable to test meters at least twice 
per year. In some cases two meters are installed in 
parallel; such meters are a constant check upon one 
another. 

Motion Pictures. — Photography .—Cooper Hewitt 
lamps are used almost exclusively for this purpose, 
and about 50,000 c. p. are required to do good work. 
Lamps must be arranged adjustable to suit whim of 
producer. 

Exhibition .—The exhibition of motion pictures may 
be carried on with one arc lamp, but it should have 
an adjustable rheostat or compensator. Many films 
are very dark, and require extra strong lighting. 
Good exhibitions require at least two machines and a 
corresponding number of arc lamps, one to be ready 
when the other runs out. Stereopticon lamps and 
spot lights must also often be provided for. It is 
customary to require at least a No. 6 wire for each 
motion picture arc, as they often draw as high as 50 
amperes. There is considerable fire and life hazard 
connected with the exhibition of motion pictures, and 
each municipality usually has some rules governing 
the handling of films and apparatus, which should be 
consulted. 

Motors. —Alternating Current .—There are four 
general types of alternating current motors; viz., in¬ 
duction, series, repulsion and synchronous motors. 

Induction Motors .—The stationary part of this 
motor is termed the “ stator, ” the moving part the 
“rotor.” That part of the winding which receives 
current from the supply line is known as the “ pri¬ 
mary,’ ’ the other as the “secondary.” From a me¬ 
chanical point of view this is the simplest and best of 
all motors, and it is also the most used type. Poly¬ 
phase induction motors are self-starting, but single¬ 
phase motors require some special starting device. 
These motors are essentially constant speed motors, 


ELECTRICAL TABLES AND DATA 


145 


but their operation depends upon the “slip,” which 
requires a slight reduction of speed with increasing 
load. This motor has a poor starting torque and often 
requires four or five times the running current to 
start it. 

The rotor of the common induction motor is not 
provided with any winding, but for special purposes,, 
such as printing presses, cranes, etc., wound rotors 
are often used. Resistances can be used with such 
motors and the speed also thus controlled. The speed 
will, however, be variable with the load and the motor 
will require watching. With a wound armature the 
torque is the same for all speeds. Auto-starters, or 
compensators, are used to start the larger motors, but 
the smaller ones may be connected directly to the 
circuit. A throw over switch fused on one side only, 
and so connected that the starting current need not 
pass through the fuses, is generally used for medium 
size motors, up to 5 H. P. 

The synchronous speed of an induction motor can 
be found by the formula: 


R. P. M. = 


60 x frequency 
number of pairs of poles 


Below is a tabulation of all possible speeds of syn¬ 
chronism of 60 and 25 cycle motors with the numbers 
of poles given: 


Number Foies 

60 Cycles 

25 Cycles 

2 . 

. 3600 

1500 

4 . 

. 1800 

750 

6 . 

. 1200 

500 

8 . 

. 900 

375 

12 . 

. 600 

250 

16 . 

. 450 

1871/2. 

24 . 

. 300 

125 


Actual speeds, on account of “slip,” are from 3 to 
10 per cent lower. 










146 


ELECTRICAL TABLES AND DATA 


Repulsion Motor .—The field winding of this motor 
is similar to that of a single-phase induction motor. 
There is no connection whatever between it and the 
armature, and the latter is always wound and pro¬ 
vided with a commutator and short-circuiting brushes. 
The currents induced in the armature always tend to 
oppose those in the field, hence the name, repulsion 
motor. The speed of this motor is variable with the 
load and may be above synchronism, but the operation 
at this speed is not satisfactory. In some types the 
direction of rotation, speed, regulation, and stopping 
and starting may all be accomplished by simply shift¬ 
ing the brushes. Some single-phase motors are ar¬ 
ranged to start as induction repulsion motors. When 
the motor is up to speed, the brushes are automatically 
thrown off, and the motor continues to run as a sim¬ 
ple induction motor. The starting current of this 
type of motor is from two to three times the full load 
current and the starting torque is good. 

Reversing Direction of Rotation .—The synchronous 
motor is not self-starting, and will run in whichever 
direction it is started. It is usually started by a small 
induction motor, and to reverse its direction of rota¬ 
tion the connections of the latter must be changed. 
Polyphase synchronous motors may be started by turn¬ 
ing on the a. c. current while the d. c. fields are open. 
In such a case the direction of rotation can be changed 
by reversing two-phase wires in the same manner that 
induction motors are reversed. To reverse the direc¬ 
tion of rotation of a two-phase motor, the two wires of 
one phase must be changed. If there are only three 
wires the connections must be changed so that the 
relative direction of current through one of the phases 
is reversed. 

Three-phase induction motors are reversed by 
changing the connections of any two-phase wires. 
The direction of rotation of a single-phase induction 


ELECTRICAL TABLES AND DATA 


147 


motor is indeterminate unless it is provided with some 
special starting apparatus. Some may be started by 
hand and will run in whichever direction they are 
started; others require that the connections of the 
starting coils (not starting box) be reversed. The 
alternating current series motor may be reversed in 
the same manner as d. c. motors. The repulsion motor 
may be reversed by either shifting the brushes or re¬ 
versing the field connections. 

Series' Motor .—This type of alternating current 
motor has about the same general characteristic as the 
direct current series motor. Except in small sizes it 
cannot be used without constant attendance. The field 
magnets are always laminated and the fields must be 
obtained with as few turns of winding as possible, as 
the self-induction increases as the square of the num¬ 
ber of turns of wire. Series motors may be had for 
use either on alternating or direct current circuits. 

The armature is relatively more powerful than the 
fields, and the field distortion is therefore greater than 
in direct current series motors. To regulate this, 
many of the motors are provided with extra coils, 
some of which are in series with the fields and arma¬ 
tures, and others arranged to receive current only by 
induction. 

Synchronous Motors .—These motors may be either 
single of polyphase. They must run at an absolutely 
constant speed governed by that of the generator. 
This speed may be found by the formula 

^ 60 x frequency 

R. P. M. =--r-^- tt—^— 

number ot pairs ot poles 

All synchronous motors require direct current for 
field excitation. They are not self-starting in the true 
sense of the word, and must be brought up to nearly 
the proper speed before current is finally turned on. 




148 


ELECTRICAL TABLES AND DATA 


Synchronous motors are not much used, but where 
they are used they may be made to exert a beneficial 
effect upon the power factor of the line. They cannot 
be made to start under load, and if overloaded will 
come to a stop. “Hunting’' or “phase swinging” is 
one of the chief troubles encountered with synchronous 
motors. The two chief objections to synchronous mo¬ 
tors are: they require direct current for field excita¬ 
tion, and skilled attendance for starting. 

Starting of a . c. Motors .—Most sjmchronous motors 
are started by small induction motors and gradually 
brought up to the speed of synchronism. A synchro¬ 
scope is usually provided to determine when the proper 
moment to throw in switch has arrived. 

Polyphase synchronous motors may be made self¬ 
starting by opening the field circuit and allowing the 
line currents to pass through the armature. The arma¬ 
ture then creates its own fields, and begins to revolve 
on the principle of an induction motor. The speed 
gradually increases, and when it reaches about that of 
synchronism, the d. c. field circuit is closed. Where 
motors are started in this way, an ammeter should be 
in the circuit and the current observed. If the current 
grows less after the field circuit is closed, the motor is 
working properly; if otherwise, the switch must be 
opened again, and a new trial made. This method of 
starting should not be used unless it is known that the 
motor is arranged for it. Very high potentials may 
be induced and break down the insulation. 

The starting current of induction motors thrown 
directly onto the line is from three to ten times the 
normal running current, and to keep it from becom¬ 
ing excessive, compensators or auto-transformers are 
usually inserted in the line wires. This provides low 
voltage for starting. There are usually either three 
or four taps in the connections of an auto-transformer. 
When only three are provided it is customary to 


ELECTRICAL TABLES AND DATA 


149 


arrange them to give 50, 65, and 80 per cent of the 
line voltage. Four taps are used only with the 
largest motors and in such a case the taps are ar¬ 
ranged for about 40, 58, 70, and 80 per cent of the 
line voltage. Always make the connection for the 
lowest voltage at which the motor can be started. 
Modern starters are equipped with no-voltage and 
overload releases. 

Three phase motors may be connected either in 
star or delta. If the latter is the permanent connec¬ 
tion the switching arrangement may be such as to put 
the motor in star for starting, the switch being thrown 
over when the motor has attained some speed. In 
cases where the three transformers are near the motor 
the transformer connections may be switched in the 
same way, using the star connection to start the motor 
and throwing over to delta when it has gained some 
in speed. 

Medium sized motors are often connected direct to 
the line without any means of reducing the voltage. 
In such cases a throw-over switch unfused on one 
side, but properly fused on the other, is provided. 
The switch is closed on the unfused side until the 
motor has attained its speed and is then thrown over 
to bring it under the protection of the fuses. With 
this arrangement the fuses at motor may be provided 
to fit the running current while those at the beginning 
of supply line must be large enough to stand the 
starting current which is often very excessive. 

Speed Control .—The speed of a synchronous motor 
is unchangeable and governed entirely by the fre¬ 
quency and number of poles. The speed of an induc¬ 
tion motor varies directly as the frequency, and if we 
have means of changing this, we may obtain any 
speed desired. 

The same formula for speed which shows the. above, 
also shows that the speed can be varied by varying the 


150 


ELECTRICAL TABLES AND DATA 


number of poles. This is sometimes accomplished by 
switching devices which combine poles so as to reduce 
their number by one-half. This method is not much 
used. 

The speed can also be altered by changing the volt¬ 
age applied to the motor. A fourth method of speed 
control consists in providing a wound armature in 
place of the ordinary squirrel cage armature and 
placing resistances in the armature windings. Some¬ 
times these resistances are located inside of the arma¬ 
ture spider, at other times the leads are brought out, 
and the resistances mounted outside of the machine. 
The loss in speed of an induction motor with increas¬ 
ing load is proportional to the resistance in the rotor 
circuit, and if carried too far will cause the motor to 
stop. A reduction in speed of from 15 to 20 per cent 
will cause the ordinary squirrel cage motor to stop, 
but with a wound rotor the variation may be much 
greater. The speed control of a. c. motors is never 
very satisfactory, but where it must be, the wound 
rotor method is the most practical. 

Variable Speed Arrangements of Motors .—A well 
known method of obtaining various speeds is that 
known as the “tandem,” “cascade” or concatenation 
method of coupling two motors together to obtain 
variable speed. The first motor is fed direct from the 
line through suitable starters and the currents in the 
second motor are produced in the wound rotor of the 
first. The rotor of the second motor is also wound 
and equipped with controlling resistances. Four 
speeds are obtainable. First, the natural speed of 
motor 1 running alone; second, that of motor 2 run¬ 
ning alone; third, the speed of the two motors com¬ 
bined when both tend to revolve in the same direction, 
and fourth, the speed of the two motors combined 
when one tends to run in the opposite direction. 

Connected in direct concatenation (both motors 


ELECTRICAL TABLES AND DATA 


151 


tending to run in the same direction) the speed can 
be found by the formula 


R.P.M.= 


60 x frequency 


number of pairs of poles on both machines 


When one of the rotors is connected to oppose the 
other the speed is 

60 x frequency 


R. P.M.= 


difference in number of poles in the two 

machines 


If the number of poles on the two machines is the 
same, they will run at half speed when connected in 
direct concatenation. 

This method of control is not of much use with fre¬ 
quencies above 25 cycles on account of a low power 
factor. With this method a wound rotor is also 
always employed. 

Motor Testing .—Motors may be tested to determine 
their capacity in H.P. or K. W.; their insulation 
resistance; their heating; speed regulation, and 
efficiency. 

The H.P. capacity of a motor, other things being 
equal, depends entirely upon the current which the 
armature will stand, and this, assuming proper me¬ 
chanical construction, depends entirely upon the heat¬ 
ing. The heat generated is proportional to the square 
of the current, but the temperature of the wire is 
influenced considerably by the ventilation. The tem¬ 
perature also depends upon the length of time the 
current is used, and therefore the actual H. P. which 
any motor may develop depends very much upon 
whether it is to be used continuously or intermittently. 
Every motor thus has two ratings. 

The continuous rating of a motor is at present 
usually taken as the output in H. P., or K.W. which 
it can deliver continuously, with a maximum rise in 




152 


ELECTRICAL TABLES AND DATA 


temperature above the surrounding air at 25° C. 
(77° F.) of not more than 40° C. (104° F.) on field 
and armature, and not more than 55° C. (131° F.) on 
commutator. The intermittent rating differs from 
this in that it allows a temperature rise of 65° C. on 
field and armature and 90° on the commutator to be 
attained in an hour’s run. Motors designed to fulfill 
these requirements can be given a still higher over¬ 
load rating to be used in connection with apparatus 
which is in operation for only a few minutes at a 
time. The test for heating is made by a thermometer 
placed upon the parts and covered with waste to shut 
out the cooling influence of the air. The places of 
highest temperature should be selected. 

The H. P. output of a motor may be found by the 
well-known prony brake test. To make the test, adjust 
the screws until the motor speed is reduced sufficiently 
to allow the desired current through the armature. 
The H. P. of the motor can then be found by the 
formula: 

TT P _ sxlxp 

33,000 

where 5 = speed of pulley; 1 = length of lever from 
center of pulley to scale attachment, and p = the pull 
on scales in pounds. 

The II. P. delivered to the motor is equal to the 
product of volts and amperes, and dividing the H. P. 
developed by the motor by that delivered to it, will 
give us the efficiency. The prony brake test cannot 
well be continued long enough to test heating of 
motor, and some other form of load must be placed 
upon it. The speed regulation of a motor may be 
found by operating the motor at various loads from 
zero to maximum, and noting the changes in speed. 
In testing alternating current motors we must mul¬ 
tiply the product of volts and amperes by the power 



ELECTRICAL TABLES AND DATA 


153 


factor, or use a wattmeter instead of volt and am¬ 
meters. The starting torque of a motor can be found 
in the same way as we found the II. P., but we must 
adjust the screws until the armature comes to a 
standstill. 

Motor Troubles .—If the fuses blow at starting , 
contacts may be loose or dirty, or the fuses are of 
insufficient capacity. The motor may be overloaded 
or out of order in some way. The brushes may not 
be properly set. The rheostat may be manipulated 
too fast. It is usual to allow about 30 seconds to pass 
during the starting of the ordinary motor. The sup¬ 
ply voltage may be higher than the motor is intended 
for, or the rheostat may be too large, and not intro¬ 
duce sufficient resistance. The motor may be im¬ 
properly connected. The field circuit may be open. 
This would prevent the armature from generating the 
necessary counter e. m. f. There may be a short cir¬ 
cuit in the armature, or in the fields. If a short cir¬ 
cuit cuts out part of the field, it will indicate itself by 
undue heating and prevent the armature from pick¬ 
ing up. If the frequency is too low, there will be an 
excessive current; if it is too high, there will be 
insufficient current. 

If motor fails to start and the fuses do not blow, 
there may be a dead line; test for current. 

In the case of a series motor there may be an open 
circuit in either armature or fields; this can be in the 
armature only if a shunt motor. Insufficient tension 
or poor contacts of brushes also often prevent the 
motor from starting. In an alternating current motor 
the frequency may be too high. One or more phases 
may be open. 

Fields Running Hot. —The voltage at which ma¬ 
chine operates may be higher than that for which it 
was intended. Fields may be in parallel where they 
were meant to be in series. A part of the field may 


154 


ELECTRICAL TABLES AND DATA 


be short circuited, or cut out by grounding. In such 
a case one of the fields will be cool while the other runs 
abnormally hot. 

Heating of Armature. —This may be caused by an 
overload; the heating increases as the square of the 
current used. There may be a short-circuited arma¬ 
ture coil; if so, it will speedily show itself by burning 
out. A strong odor of heated shellac will probably be 
the first indication. Poor ventilation is often the 
cause; many motors are meant to operate either open 
or enclosed, and the enclosed capacity is always much 
less than the open. 

Shaft of Bearings Banning Hot. —This may result 
from improper oiling, boxes too tight, shaft bent, belts 
too tight, rough bearings, or the armature may not 
be properly centered, and thus press too hard on one 
of the end collars. 

Shocks Obtained- from Machine. —These may be due 
to static electricity or to grounding of some live part 
of the motor or the frame. The troubles from static 
electricity can be overcome by grounding the frame 
or fitting the belting with arresters. 

Sparking of Brushes. —This may be due to wrong 
position of the brushes. With increasing load, the 
brushes of motors must be shifted against the direc¬ 
tion of rotation, and, vice versa, with generators the 
opposite rule holds. The best motors, however, re¬ 
quire very little shifting of brushes. Rough commu¬ 
tator, ragged brushes, or dirty condition of either 
commutator or brushes are frequent cause of spark¬ 
ing. Insufficient tension is also a frequent cause of 
sparking. If the brush is too narrow it will leave one 
segment before making the proper connection with the 
next; if too wide, it will short circuit too many and 
thus cause sparking. Incorrect spacing of brushes 
will cause sparking. Compound wound motors, or 
those operating with light field, are subject to much 


ELECTRICAL TABLES AND DATA 


155 


sparking. To prevent this, inter-poles are often pro¬ 
vided. Test direction of current in series winding by 
starting motor with shunt field open. An open circuit 
in an armature coil will cause severe sparking, which 
will occur only at a certain place on commutator. 

Motors. — Direct Current .—There are three types 
of d. c. motors; viz., series, shunt, and compound. 

The Series Motor .—Small series motors, such as fan 
motors, can be made to work successfully under any 
conditions. Large series motors with a variable load 
require constant attendance. Lightening the load 
will allow the motor to speed up inordinately and be¬ 
come dangerous. Such motors are very useful where 
heavy loads are to be started, as the torque is the¬ 
oretically proportional to the square of the current as 
long as the fields are at a low point of saturation. 
And in all cases w r hen the fields are not fully satu¬ 
rated, the torque increases faster than the current. 
The maximum torque exists at low speed and is inde¬ 
pendent of the voltage, depending entirely upon the 
current. 

Shunt Motors .—The shunt motor is the most used of 
all direct current motors, and if properly constructed 
operates at a fairly uniform speed for all loads within 
its capacity. Once started it requires no attention. 
It is suitable for all classes of work, except such as 
street car service where the current is often suddenly 
interrupted and as suddenly thrown on again by 
accidents to the trolley. Its starting torque is not 
as good as that of the series motor, but it is fair. The 
field strength varies with the voltage, but as long as 
this is maintained it is independent of the voltage at 
armature terminals. 

The Compound Motor .—This is a combination of 
shunt and series motor and has both windings. If 
the current in the compound winding is in the same 
direction as that in the shunt, the increased current 


156 


ELECTRICAL TABLES AND DATA 


strength necessary to handle a heavy load will 
strengthen the fields and slow the motor down. Such 
a motor is known as “cumulative” and has a very 
good starting torque. If the compound winding is in 
the opposite direction, an increased current will 
lighten the fields and cause the motor to speed up, but 
will give it a poor starting torque. The compound 
winding may be so adjusted that the motor will run 
at a very even speed for all loads within its capacity. 
A motor so connected is known as “differential.” 
Owing to the fact that part of the field magnetization 
is destroyed by the series winding, the efficiency is 
somewhat low. Commutating or inter-poles are often 
inserted in d. c. motors. Such poles are provided to 
overcome the armature reaction and produce sparkless 
commutation. Motors so equipped can carry greater 
overloads. They are very useful where a good start¬ 
ing torque is required. Motors are further divided 
into open and enclosed types. The capacity of a 
totally enclosed motor is only about 60 per cent of 
that of the open motor. The capacity in H. P. depends 
upon whether the motor is to be used continuously or 
intermittently, and is governed by the heating limita¬ 
tion, the heat generated being proportional to I 2 . 

The current required by any motor can be found 
by the formula 

~ , H. P. delivered x 746 

Current = —-=-- 

efficiency x voltage 

The efficiency of a motor can be found by dividing 
the input by the output. All motors are delivering 
their maximum power when the speed is such that the 
counter e. m. f. of the motor is one-half of that deliv¬ 
ered at the terminals. 

Reversing Direction of Rotation .—All d. c. motors 
may be reversed by changing the connections of either 
field or armature so that current passes through one 



ELECTRICAL TABLES AND DATA 


157 


of them in the opposite direction. If the current in 
both is reversed the direction of rotation will remain 
as before. Most multi-polar motors may be reversed 
by shifting the brushes sufficiently; this is equivalent 
to reversing armature leads. 

Speed Control .—All d. c. motors tend to run at a 
speed which enables the armature to generate a 
counter e. m. f. equal to that of the supply. The speed 
can be varied by strengthening the field, which re¬ 
duces it, or weakening the field to increase it. The 
commonest method of accomplishing speed control is 
by means of resistance cut into the armature circuit. 
This method, however, causes a speed variable with 
the load, the fall in pressure at the motor terminals 
being equal to 1R. Adjusting the field strength to 
regulate the speed causes much sparking at the 
brushes. This can be obviated to a large extent by 
the use of commutating or inter-poles. The armature 
current passes around these and tends to keep the 
neutral point at a certain place, thus preventing 
sparking. Speed control is further effected by switch¬ 
ing arrangements which enable one to connect several 
motors either in series or parallel; the parallel con¬ 
nection giving the higher speed and the series the 
lower. Such systems are used mostly in connection 
with d. c. street railway service. 

Starting of d. c. Motors .—All d. c. motors, except 
the small ones which are wound with a high resistance 
in armature circuit, require some extra resistance to 
keep the current down until the armature has attained 
sufficient speed to generate the counter e. m. f. which 
finally limits the current. This resistance must never 
be in the field circuit of a shunt motor, but always in 
the armature circuit. In the differential motor, the 
series winding should be cut out of circuit until the 
motor is started, otherwise the excessive starting cur¬ 
rent will weaken the field too much. In the cumu- 


j58 


ELECTRICAL TABLES AND DATA 


lative type of motor, the series field adds to the start¬ 
ing torque. A motor may be tested as to whether it 
is cumulative or differential by starting it with the 
shunt field open. If cumulative it will run in the 
same direction as with the shunt field closed. The 
starting resistances of shunt motors are usually wound 
with fine wire which will overheat and burn out if 
left in circuit too long. Not more than thirty seconds 
should be consumed in manipulating the handle. In 
some cases, however, special apparatus is provided 
which can carry the current indefinitely. If motor 
does not start at once, open switch and look for the 
cause of trouble. 

Power Required to Operate Machinery .—When the 
H. P. needed to operate a given machine is not known 
it may in some cases be calculated from the formula: 

TT _ P x2vxrxn 
12x33,000xe 

where P =pull in pounds which must be applied at 
periphery of pulley to move it; r— radius of pulley in 
inches; n = number of revolutions per minute; e -the 
efficiency of a direct current motor or the product of 
efficiency and power factor in an alternating current 
motor or circuit. 

If the machinery to be started is equipped with 
heavy flywheels, or possesses considerable inertia of 
any kind, the size of the motor needed is governed by 
the starting requirements which depend largely upon 
the rate of acceleration demanded. In connection 
with other machinery, such as ventilating fans for 
instance, the power required increases faster than the 
speed and can be measured onty when the device is 
operating at full speed. For such motors the above 
formula cannot be used and it is necessary to obtain 
data from manufacturers or other users. 



ELECTRICAL TABLES AND DATA 


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To find H. P. required, multiply pull in pounds at periphery of pulley by number 
found where the given speed and radius cross. 


















160 


ELECTRICAL TABLES AND DATA 


In the table below the values of —— — 

12 x o3,000 x e 

(e being assumed as of about .75) are given wherever 
the horizontal line pertaining to speed crosses with a 
vertical line pertaining to radius of pulley. 

Care must be exercised in determining P; it must 
not be more than just enough to cause motion, and at 
best can be only an approximation. P may be deter¬ 
mined by a spring balance, or by a weight and lever. 
If the latter is used and attached to rim of pulley, 
multiply weight by distance from center of pulley 
and divide by radius of pulley. 

Group vs. Individual Drive. —The total H. P. ca¬ 
pacity of motors for individual drive must be equal 
to the H. P. demands of all the machinery. 

The H. P. capacity for group drive may be con¬ 
siderably less, because not all of the driven machinery 
is used at the same time. How much of saving there 
is in any given case depends upon circumstances. 
Very often the shafting necessary with group drive 
requires as much additional H. P. capacity as is saved 
by the other consideration above. 

The total H. P. required for group drive can be 
found by the formula: 

p — (^ • P • ^ /) ~t~ s 

e 

where h.p. is the horsepower demanded by the total 
machinery if run all at the same time; / is the load 
factor; s the H.P. required to drive shafting, and e 
the efficiency of the motor. The large motors used for 
group drive are more efficient at full load than the 
smaller ones, but a group drive motor is seldom run 
at full load. If it is properly chosen it will be over¬ 
loaded part of the time and inevitably be running 
with no other load than the shafting part of the time. 




ELECTRICAL TABLES AND DATA 


161 


The nearer it can he kept running with full load the 
more efficient it will be. The total H. P. required for 
individual drive is equal to the sum of the H. P. of 
all the machines divided by the efficiency. The full 
load efficiency of the small motors is lower, but there 
is never any idle machinery or shafting to be moved, 
and if properly selected the motors may operate at 
full load efficiency most of the time. In most cases 
individual drive is the most economical where a per¬ 
manent installation is considered, but the cost of 
installation is generally somewhat higher. In addi¬ 
tion to the above advantages, which can be figured out 
in dollars and cents, the following considerations 
should be of interest and duly noted: With indi¬ 
vidual drive the fire and life hazard are somewhat 
increased, but the shafting and belting accidents are 
greatly decreased. In connection with low voltage 
(110 or 220) the life hazard is small, and the advan¬ 
tage is on the side of the individual drive. With 
high voltage group drive is probably safer. With 
individual drive the facilities for speed regulation are 
better and motor troubles cannot throw a whole shop 
out of order. There is no shafting to cause dirt and 
noise and interfere with illumination, and there is 
less vibration in the workroom. Individual drive, 
however, requires somewhat more care and atten¬ 
tion. 

Where we have the choice of motors of different 
efficiencies we can afford to expend for the motor of 
the better efficiency a sum of money upon which the 
annual interest charge will be equal to the saving in 
the cost of energy effected by the better motor. We 
must, however, select the rate of interest so as to 
cover all depreciation, and if we assume that. the 
motor will be a dead loss at the end of the time it is 
to be used, we shall obtain the following rates of 
interest, using a 6 per cent basis: 


162 


ELECTRICAL TABLES AND DATA 


Motor to be used 1 year only, 

106 

per cent 

2 yeai*s, 

56 

< < 

3 years, 

40 

< t 

4 years, 

32 

( < 

5 years, 

27 

(( 

6 years, 

24 

t < 

7 years, 

21 2 

< i 

8 years, 

20 

< i 

9 years, 

18} 

i i 


For longer periods of time the interest rate decreases 
slowly and the above will cover all ordinary cases. 

According to the above principles we can determine 
the amount of money we may economically invest in 
order to substitute a motor of higher efficiency for 
another with lower efficiency by the formula, 



K. W. x r x h x d x e 
per cent interest 


where C = capital to be invested; K.W.=the number 
of watts used; r=the rate per K. W. hour; h=th.e 
number of hours K.W. is used per day; d = the num¬ 
ber of days per year; e = the difference in efficiency of 
the two motors; per cent interest = the rate of interest 
governed by the number of years motor is to remain 
in use as given above. 

In the following table it is assumed that the motor 
will be used 300 days per year, and on this basis the 
numbers given represent the capital which could prof¬ 
itably be invested with K. W., r, and h equal to unity, 
and e and the rate of interest as given in the table. 
To use the table for determining how much can prof¬ 
itably be invested to substitute a more efficient motor 
in place of a poorer one, it is but necessary to find the 
product of K.W. xrxh, and with this multiply the 
number found where the horizontal line pertaining to 
the difference in efficiency in favor of the better motor 




1.874 2.222 2.500 2.792 3.000 3.200 




ELECTRICAL TABLES AND DATA 


163 


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TABLE XXXXVIII— Continued 


164 


ELECTRICAL TABLES AND DATA 


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ELECTRICAL TABLES AND DATA 


165 


crosses with the rate of interest applicable to the 
problem. The result will be the sum in dollars and 
cents which can with profit be expended to procure 
the better motor. 

Rule of Table .—Find the difference in efficiency 
between the motors considered and the number of 
years the motor is to be used. Select the number 
found in the longitudinal line where the correspond¬ 
ing efficiency (given in vertical column at the left) 
crosses with the proper rate of interest (given at top) ; 
multiply this number by the K. W. hours per day, and 
by the rate per K. W. The result will give the amount 
of money which may be invested to procure the motor 
of higher efficiency. If this sum will make up the 
difference in cost, the better motor should be provided. 

Nails.—Use cut nails for driving into brickwork. 


TABLE XXXXIX 
Dimensions of Nails 


Common Nails 


Size 

Length 

Nearest 

B. & S. 

Diam. 

in 

inches 

2d 

1 

13 

%28 

3d 

m 

12 

%4 

4d 

i y 2 

10 

%4 

5d 

i% 

10 

%4 

6d 

2 

9 

%4 

7d 

2 y 4 

9 

%4 

8d 

2 y 2 

8 

17 /i28 

9d 

2% 

8 

1 %28 

lOd 

3 

7 

19 /{28 

12d 

3 y 4 

6 

1 %28 

16d 

3 y 2 

6 

%2 

20d 

4 

4 

25 A 28 

30d 

4 y 2 

4 

2 %28 

40d 

5 

3 

2 %28 

50d 

5 y 2 

2 

31 /l28 

60d 

6 

2 

3 %28 


Finishing' Nails 


Approx. 


Diam. 

Approx. 

number 

Nearest 

in 

number 

per lb. 

B. & S. 

inches 

per lb. 

876 

14 

%28 

1351 

568 

13 

%28 

807 

316 

13 

%28 

584 

271 

13 

9 A28 

500 

181 

11 

%2 

309 

161 

11 

%2 

238 

106 

10 

%4 

189 

96 

10 

%4 

172 

69 

9 

%4 

121 

63 

9 

%4 

113 

49 

8 

17 /i28 

90 

31 

8 

1 ’^i28 

62 

24 




18 




14 




11 





166 


ELECTRICAL TABLES AND DATA 


National Electrical Code (Abbreviated N.E.C 7. 
—The N. E. C. contains the recommendations of the 
National Fire Protection Association in reference to 
electrical installations. It is revised every two years, 
and its recommendations are generally accepted as 
standard throughout the United States. Most mu¬ 
nicipalities pattern their regulations after this code, 
but introduce a few variations which local conditions 
seem to warrant. The National Board of Fire Under¬ 
writers issue ‘ ‘ The List of Electrical Fittings. ’ ’ This 
contains a list of appliances which have been tested 
and are considered safe. Those engaged in electrical 
construction work are advised to keep in touch with 
the N. E. C., the List of Electrical Fittings, and local 
requirements. 

Nernst Lamp. —This lamp is not as much used as 
formerly. It has a high intrinsic brilliancy; requires 
no reflectors; should be hung high. It requires con¬ 
siderable attention to keep in repair and cannot be 
used in theatres or similar places where quick changes 
are necessary. 

Neutral Wire. —This term describes one of the 
three wires used in connection with the three-w r ire 
system. Normally this wire carries no current and 
is, therefore, often smaller than either of the outside 
wires. In case an outside fuse blows, it may, however, 
be called upon to carry the full load current. It is 
always fused higher than the outside wires, and often 
is not fused at all. Blowing of the neutral fuse may 
do much damage. Ordinarily this wire is also 
grounded. 

In a star connected polyphase system, the point at 
which all of the wires connect is also spoken of as 
neutral. The fourth wire in a three-phase system 
may also be so termed. 

Non-Inductive Load. —A non-inductive load is dis¬ 
tinguished from an inductive load by the fact that 


ELECTRICAL TABLES AND DATA 


1G7 


the current is in phase with the voltage. Circuits 
supplying only incandescent lamps are very nearly 
non-inductive; arc lamps and motors make up a 
strongly inductive load. 

Office Lighting. —Desk lights are very common, 
but they are also a nuisance. They cause constant 
annoyance, and increase the fire hazard. 

Inverted lighting is very favorably received in many 
offices and deserves extended trials. The newer high 
efficiency lamps have done much to make it econom¬ 
ical. Where all employes are constantly at their desks 
there can be no difference of opinion regarding the 
superiority of a good general illumination in every 
respect. Local illumination can appear advisable only 
in such places where most of the desks are occupied 
for a short time per day only. 

Avoid large spreading chandeliers carrying many 
lamps. These often cause a multiplicity of shadows. 
If clusters are used, lamps should be close together. 
Do not run wires in any but the main walls or parti¬ 
tions; use three-fourths inch conduit so as to have 
plenty of capacity for changes which are always tak¬ 
ing place. Arrange lighting to harmonize with win¬ 
dows, so that furniture placed correctly for daylight 
will also fit the artificial illumination. 

Ohm. —The international ohm has been legalized 
in this country and is defined as the resistance which 
a column of mercury of a uniform cross section, at 
the temperature of melting ice, and 106.3 centimeters 
in length, and of a mass of 14.4521 grams, offers to an 
unvarying electric current. 


Ohms Law.— 



I xR = E;R = 


E 


Ohmic Loss or Drop. —The loss in e.m.f. or drop 

in p. d. caused by the resistance as distinguished from 
that caused by reactance. 


168 


ELECTRICAL TABLES AND DATA 


Overhead Construction. —The timbers most in use 
for poles are: Michigan cedar, Western cedar, chest¬ 
nut, pine and cypress. Of these the cedars and 
chestnut are the most used. The cedars are easier to 
climb and the taper is greater so that the tops of 
cedar poles are smaller in proportion to the butts than 
chestnut poles. On account of the variable nature of 
the wood and the fact that they soon begin to rot at 
the ground line, which is the point of greatest strain, 
the strength of poles must be calculated with a large 
factor of safety. In the tables following the breaking 
strain of the wood has been taken as 7,000 pounds 
per square inch and a factor of safety of 10 has been 
used. 

Poles are usually designated by their length in feet 
and diameter at top in inches; thus a pole 40 feet 
long and 8 inches in diameter at top is spoken of as a 
40-8 pole. The standard or most used pole is 35 feet 
long and has a 7-inch top. In swampy places poles 
are often set in concrete. 

Poles should be set with the sweep in the line so 
that the wires may be straight. Use no iron poles 
where lines must be worked on while alive. Set pole 
steps 32 inches apart and stagger them. In cities 
place poles on lot lines. Avoid placing poles near 
lamp posts, hydrants or catch basins. Give corner 
poles a slight rake outward. Use the heaviest poles 
for transformers. Special attention should be given 
to tamping at bottom and top of holes, and the earth 
should be piled up a little around pole to keep water 
from running in. Keep one side of pole free for 
climbing. Double arm all poles subject to unusual 
strains. The lowest cross arm should be at least 18 
feet above ground and 22 feet above railway tracks. 
Allow at least 2 feet between cross arms; more if pos¬ 
sible. Insulate guy wires. Make cross arms of uni¬ 
form length. 


ELECTRICAL TABLES AND DATA 


ltf9 


Standard cross arms are rounded on top; 3| inches 
wide by 4^ inches high; allow 24 inches between pole 
pins, and at least 12 inches between other pins; this 
distance varies with number of pins, length of span 
and voltage. Junction arms usually have a wider 
spacing between inside pins. The high tension wires 
should be carried on the top arms; secondary wires 
are usually run below them, and the lowest arms are 
left for signal wires if any are to be run on same line. 
There should be a space of about five feet between the 
signal and the lighting and power wires. The lowest 
voltage wires are usually run next to poles; circuit 
wires should be kept together, and neutral of three- 
wire system should be run in center. The fourth wire 
of a three-phase system is also carried next to pole. 

Pole Line Calculations .—The first step in laying 
out a pole line must be to decide upon height of poles 
and maximum span lengths. The next step will be 
to calculate the strains to which poles may be sub¬ 
ject. The main body of a pole line is subject only to 
wind pressure, and this can be determined by use of 
Table LII. End poles are subject to half of this wind 
pressure and strain from the wires as well. Poles 
from which taps are taken have the full wind pressure 
and strain of wires leading off. Corner poles must be 
considered as subject to 1.41 times the strain on end 
poles. The wire strains upon poles can be found by 
the use of Table LI. The strains upon poles having 
been determined, the proper diameter at ground line 
can be determined by Table LIII. 

When the strains on a pole are found to be greater 
than a pole of desirable diameter can well bear, it 
must be reinforced by guying or bracing. The proper 
diameter of guy cables can be found from Tables 
LV to LVII. If the pole is light compared to the 
strain put upon it, it will be best to provide a guy 
cable to take care of the total strains. 


170 


ELECTRICAL TABLES AND DATA 


TABLE L 


It is common practice to string electric power wires 
in accordance with the following tabulation, which 
gives the sag in inches: 


Length 

of 

span 

20 ° 

30° 

Temperature 
40° 50° 

in Fahrenheit 
60° 70° 

o 

O 

oo 

90° 

50.... 

8 

8 

9 

9 

10 

11 

11 

12 

60.... 

9 

10 

11 

11 

12 

13 

14 

14 

70.... 

10 

11 

12 

13 

14 

15 

16 

17 

80.... 

12 

13 

14 

15 

16 

17 

18 

19 

90... . 

14 

14 

16 

17 

18 

19 

20 

21 

100 .... 

16 

16 

17 

19 

20 

21 

23 

24 

110 . ... 

18 

18 

19 

21 

22 

24 

25 

26 

120 .... 

18 

19 

21 

23 

24 

26 

27 

28 

130.... 

20 

22 

24 

26 

28 

30 

32 

33 

140.... 

22 

23 

26 

28 

30 

32 

34 

35 

160.... 

24 

26 

28 

30 

32 

34 

36 

38 


With wires strung according to the above tabula¬ 
tion each wire at the lowest temperature given will 
cause a strain on poles as given below. To find total 
strain on pole multiply proper number in table below 
by number of wires. By allowing a greater sag the 
strain will be proportionately reduced. 

TABLE LI 

Bare Copper 

Length 


of 

Span 14 

12 

10 

8 

6 

5 

B. & 
4 

S. Gauge 
3 2 

1 

0 

00 

000 

0000 

80 

10 

16 

26 

47 

63 

80 

101 

127 

160 

202 

255 

321 

405 

512 

100 

13 

22 

34 

62 

85 

107 

135 

171 

215 

272 

343 

432 

545 

688 

120 

15 

24 

39 

70 

95 

120 

151 

190 

240 

303 

382 

481 

607 

768 

140 

18 

29 

47 

85 

116 

147 

182 

230 

294 

371 

470 

592 

740 

942 

160 

19 

32 

52 

94 

126 

160 

202 

254 

320 

404 

510 

642 

810 

1024 


Breaking Strains 

B. & S. Gauge 

Hard Drawn— 

14 12 10 8 6 5 4 3 2 1 0 00 000 0000 

219 343 546 843 1300 1580 1900 2380 2970 3680 4530 5440 6530 8260 
Annealed— 

110 174 277 441 700 884 1050 1323 1670 2100 2650 3310 4270 5320 

Insulation and sleet may easily treble the strains. 




ELECTRICAL TABLES AND DATA 


171 


The Maximum wind pressure upon the pole alone 
will range from 125 to 250 lbs., according to length 
and diameter of pole. 

The side strain on a straight pole line (125 ft. 
span) can be found by use of the table below. Multi¬ 
ply number of wires on pole by number found under 
size of wire and in proper horizontal line. 


TABLE LII 
Wind Pressure 


B. & S. 

14 

12 

10 

8 

6 

5 

4 

3 

2 

1 

0 

00 

000 

0000 

Bare wire. 

. 8 

11 

13 

19 

22 

26 

29 

32 

36 

40 

45 

50 

55 

60 

Insulated . 

.35 

38 

41 

46 

50 

53 

56 

60 

65 

70 

80 

90 

100 

110 


Sleet may easily treble these strains, but sleet seldom exists 
in stormy weather. 


TABLE LIII 

Table showing maximum strains (applied at top) 
to which poles of various heights above ground, and 


of various diameters at 
subject. 


4 

0 ) <v 


o.S 
o- g 



Height of 

Poles 

V T2 rt 

O C O 
3 C 






cj o —• 

S^.5 

20 

25 

30 

35 

40 

8. . 

147 

118 

98 

84 

74 

9. . 

209 

168 

138 

120 

105 

10 . . 

286 

228 

191 

164 

143 

11. . 

381 

304 

254 

218 

191 

12 . . 

495 

396 

330 

284 

247 

13.. 

624 

500 

416 

356 

312 

14. . 

786 

628 

524 

450 

393 

15. . 

960 

768 

640 

548 

480 

16. . 

1176 

940 

784 

672 

588 

17. . 

1407 

1124 

938 

804 

704 

18.. 

1658 

1328 

1106 

948 

828 

19. . 

1964 

1572 

1310 

1120 

982 

20.. 

2288 

1831 

1526 

1284 

1144 

21 .. 

2665 

2132 

1764 

1524 

1333 

22 .. 

3048 

2440 

2032 

1740 

1524 


ground line, should be 


Above Ground in Feet 


45 

50 

55 

60 

65 

70 

66 

58 

53 

49 

46 

42 

93 

83 

76 

70 

65 

60 

127 

115 

104 

95 

88 

81 

169 

152 

138 

127 

117 

109 

220 

198 

180 

165 

121 

141 

278 

250 

226 

208 

192 

178 

350 

314 

287 

262 

242 

224 

427 

384 

349 

320 

296 

274 

524 

470 

428 

392 

362 

336 

625 

563 

572 

469 

433 

402 

756 

664 

604 

553 

510 

474 

872 

786 

716 

655 

604 

562 

916 

915 

832 

763 

704 

652 

1144 

1066 

968 

885 

820 

762 

1356 

1209 

1108 

1016 

938 

870 


172 


ELECTRICAL TABLES AND DATA 


Depth of Setting 

Earth 5 5* 6 6 6* 6* 7 71 8 8£ 9 

Eock 4 4£ 5 5 5* 6 6£ 7 7 9* 

When erected along a curved line it is best to set 
somewhat deeper. 

TABLE LIV 


The following table probably shows the average of 
poles used for general telegraph and telephone 
purposes: 



Butt 

Top 

Wt. 


Butt 

Top 

Wt. 

Length 

Dia. 

Dia. 

App. 

Length 

i Dia. 

Dia. 

App. 

25,.. 

9 to 10 

6 to 8 

350 

50... 

9 to 15 

6 to 8 

1350 

30... 

9 to 11 

6 to 8 

450 

55... 

16 to 17 

6 to 8 

1700 

35... 

9 to 12 

6 to 8 

600 

60... 

16 to 18 

6 to 8 

2200 

40... 

9 to 13 

6 to 8 

850 

65... 

16 to 19 

6 to 8 

2500 

45... 

9 to 14 

6 to 8 

1100 

70... 

16 to 20 

6 to 8 

3000 


Guys .—Guys should be fastened to pole at point of 
strain and when so fastened the strain upon the guy 
can be found by the formula 


s= yn !± n !xp 

D 

where D = horizontal distance at ground of guy from 
pole; H= the height of guy, and P = the pull upon 
the pole. 

TABLE LY 

Table for Calculating Strength of Guys .—To find 
the proper size of wire or wire rope for guying, mul¬ 
tiply total strain upon pole by number found at 
point where line pertaining to height of guy fastening 
on pole crosses with line pertaining to horizontal dis¬ 
tance of guy at ground from pole. The product will 
equal the breaking strain of the proper cable or wire 
to be used. The table is calculated for a safety factor 
of 5. 




ELECTRICAL TABLES AND DATA 


173 


Height Horizontal distance in feet from pole to where the 
of guy guy or its support leaves ground 


on pole 

5 

10 

' 15 

20 

30 

40 

50 

10 . 

11 

7.0 

6.2 

5.5 

’5.3 

5.2 

5.1 

15. 

16 

9.0 

7.0 

6.2 

5.6 

5.3 

5.2 

20 . 

21 

11 

8.3 

7.0 

6.0 

5.6 

5.5 

30. 

31 

16 

11 

9.0 

7.0 

6.3 

5.8 

40. 

40 

21 

15 

11 

8.3 

7.0 

6.5 

50. 

50 

26 

18 

14 

9.5 

8.0 

7.0 

60. 

60 

31 

21 

16 

11 

9.0 

7.6 

70. 

70 

36 

24 

18 

13 

10 

8.5 


TABLE LYI 

Table Shewing Breaking Strain of Cables and 
Wires .—Standard Steel Strand. American Steel and 
Wire Company. Seven steel galvanized wires twisted 

into a single strand. Galvanized or extra galvanized. 

( 

Approx. 

Weight Approx. , -Galvanized Steel Wire- 


Dia. 

per 

Strength 



Break¬ 



in 

1000 

in 

A. S. & 


ing 

Nearest 


inches feet 

pounds 

W. G. 

Dia. 

Strain 

B.&S. 

Dia. 

I 

800 

14000 

12 

.106 

510 

10 

.102 

* 

650 

11000 

10 

.135 

774 

8 

.128 

* 

510 

8500 

9 

.148 

942 

7 

.144 

* 

415 

6500 

8 

.162 

1170 

6 

.162 

f 

295 

5000 

6 

.192 

1770 

5 

.182 

A 

210 

3800 

5 

.207 

2079 

4 

.204 

\ 

125 

2300 

4 

.222 

2433 

3 

.229 

& 

95 

1800 

The 

American Steel and Wire 


75 

1400 

gauge is 

commonly used for 

& 

55 

900 



iron wire. 



TABLE LVTI 

When a pole or mast is held in place by several 
guys equally spaced the figures obtained by the above 
calculation may be divided by the following guy fac¬ 
tors taken from publication of the American Steel and 
Wire Company: 












174 

ELECTRICAL 

TABLES 

AND DATA 

* 

>• guys 

Min. 

value 
of guy 

Corresponding 
line of 

Max. 
value 
of guy 

Corresponding 

£ 

factor 

action of force 

factor 

line of action of force 

3 

0.866 

30° from 1 guy 

1.000 

Opposite 1 guy or half 

4 

1.000 

Opposite 1 guy 

1.414 

way between two 

Half way between 2 guys 

5 

1.538 

18° from 1 guy 

1.618 

Opposite 1 guy or haif 

6 

1.732 

30° from 1 guy 

2.000 

way between two 
Opposite 1 guy 


Telephone Wires .—The tables below give the prac¬ 
tice of the A. T. & T. Co. No. 12 hard drawn copper 
wires are strung according to the following table: 


TABLE LVIII 


Temp. 

in 

Degrees Length of Span in Feet 


F. 

75 

100 

115 

130 

150 

175 

200 

250 

300 





Sag in 

Inches 





— 30 

1 

2 

21 

31 

41 

6 

8 

14 

22 

— 10 

1 * 

21 

3 

4 

5 

7 

9 

16 

251 

+ 10 

1 * 

3 

31 

41 

6 

8 

101 

181 

291 

+ 30 

2 

31 

4 

51 

7 

91 

12 

21 

33 

+ 60 

2 * 

41 

51 

7 

9 

12 

16 

261 

42$ 

+ 80 

3 

51 

7 

81 

HI 

15 

19 

31 

49 

+ 100 

41 

7 

9 

11 

14 

18 

221 

36 

55 


The same sag is also allowed for iron wire. 


Messenger Cables .—The standard messenger strands 
used are the following: 


Size of Cable 


No. 22 Gauge 

100 pair or smaller 
100 to 200 pair 
Larger than 200 pair 


No. 19 Gauge 

50 pair or smaller 
55 to 100 pair 
Larger than 100 pair 


Strength 
of Strand 

6000 lbs. 
10000 lbs. 
16000 lbs. 


ELECTRICAL TABLES AND DATA 175 

The above strands are about equivalent to T(D 1% 
and f inch diameters of good quality steel and used 
for spans not exceeding 200 feet. 

The sag allowed is the following: 


Span in feet 

Sag in 
inches for 
heavy cables 

Sag in inches 
when not more than 
50 pair No. 22 gauge 
wire will be used 

80 

16 

10 

90 

20 

12 

100 

22 

16 

110 

26 

18 

120 

30 

20 

130 

34 

22 

140 

40 

26 

150 

44 

30 

175 

62 

42 

200 

82 

58 


Panel Boards. —The panel board is a small switch¬ 
board, but circuits supplying more than 660 watts 
are seldom fed through it. Those described in the 
following figures and tables are designed for 660-watt 
branch circuits. Main bars have a capacity of 6 
amperes per branch circuit at 110 volts, but only 
3 amperes if designed for 220 volts. The figures in 
the tables are those furnished by the Cuthbert Electric 
Mfg. Co. Wherever the depth of cabinet required is 
the same for all numbers of circuits, it has been given 
in the fourth column from the left. In other cases 
the special designations at each height will serve as a 
guide. Where no special mark is placed and no 
depth given, the required depth is 3| inches. When 
ordering boxes, see points to be noted under 
Cabinets. 


176 


ELECTRICAL TABLES AND DATA 



( I 


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ELECTRICAL TABLES AND DATA 


177 



Figure 14.—Types of Panel Boards. 



Figure 15.—Types of Panel Boards. 























































































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181 


Plans. —Except in the case of large office build¬ 
ings, hotels, street lighting, and other large under¬ 
takings, detailed plans cannot show much more than 
location of outlets and most of the information is 
gathered from specifications. In large installations 
it is customary to designate sizes of conduit as well as 
the wires. In making the installation according to 
such plans the work is often subdivided, separate 
plans being given to different workmen or groups of 
workmen. If each group is allowed to finish its par¬ 
ticular installation a very reliable check on the labor 
performed by each man or group is obtained. 

Small plans are usually drawn to a scale of J inch, 
per foot; for large plans the scale is often -J inch, or 
even less. Details are drawn to a larger scale and 
sometimes even full size. 

Power. —This term expresses merely the rate of 
doing work. In order to obtain the quantity, it must 
be multiplied by time. Power is measured in watts 
and is usually expressed in watt hours, kilowatt hours, 
or horsepower hours, but any other length of time may 
be chosen. 

Preservation of Wood. —This is effected by impreg¬ 
nating the timber with some sort of poison which 
destroys the fungi and deprives them of food. Creo¬ 
sote is the most used, and there are various patented 
substances of a similar nature. The more thoroughly 
dried the timber is at time of application, the more 
it will absorb. Ordinarily the preservative is applied 
with a brush, but it is also applied under pressure, the 
whole pole or tie being submerged in a tank full of 
the impregnating material, to which pressure can be 
applied. 

Printing. —Printing presses are usually equipped 
with reversible and variable speed motors. For the 
larger sizes several motors are used. All of these are 
preferably fitted with remote control switches which 


182 


ELECTRICAL TABLES AND DATA 


enable the operator to govern the press from various 
points on and about it. Time is a very important 
consideration about large presses and the very best 
illumination should be supplied. On many presses 
from 10 to 20 lights are permanently installed so as to 
be ready at a moment ’s notice and obviate the neces¬ 
sity of using portable lamps. Such lights also assist 
in watching the mechanism while at work. Flexible 
conduit is serviceable, but it should be lead covered to 
guard against machine oil, which dissolves rubber. 

Composing Rooms .—A good general illumination is 
advisable in composing rooms, but there must be local 
illumination with it in certain places. In some com¬ 
posing rooms the work is of such a nature that it is 
advisable to fit each stand with a foot or arm switch 
by which a compositor can turn the light on or off 
without using his hands. 

Pumping. —One cubic foot of water weighs ap¬ 
proximately 62.5 pounds and contains about 7.5 gal¬ 
lons. One gallon weighs 8.33 pounds and contains 
231 cubic inches. If the head of a column of water is 
expressed in feet and the pressure at the foot of the 
column in pounds per square inch, then 

Head = 2.31 x pressure 

Pressure = head-r 2.31, which equals 0.434 x head, 
and this is independent of size of column. 

The H. P. required to deliver a certain quantity of 
water to a certain height is directly proportional to 
the product of the two if the so-called “friction head” 
is added to the actual height of lift. The friction 
head for various sizes of pipe and rate of flow through 
them is given in Table LXII. This friction head 
varies with the square of the velocity of the liquid, 
with the distance it flows, and with the conditions 
affecting its freedom of movement. Elbows, bends, 
burs, etc., increase it. The enormous losses in pres- 


ELECTRICAL TABLES AND DATA 


18* 


sure which take place when a small pipe is used for 
the delivery of a large amount of water can be seen 
from the table. The efficiency of centrifugal pumps 
is sometimes as low as 35 per cent, and that of rotary 
and plunger pumps ranges from 60 to 80. 

Table LXII shows the resultant net efficiency of 
motors and pumps of various efficiencies working 
together. 

From Table LXII we can take the number of cubic 
feet, pounds and gallons which one horsepower will 
lift to a height of one foot, the machinery having a 
net efficiency as given. 

Rule for Determining Horsepower Needed .—Add 
to the actual head in feet the friction head as found 
in Table LXII and multiply this by the number of 
cu. ft., lbs. or gals., as the case may be. Next divide 
this sum by the number found in same table under the 

efficiencv of the combination to be used: combined 

•/ * 

motor and pump efficiency. 

Table showing number of cu. ft., lbs., or gals, which 
can be raised 1 foot per minute by 1 H. P. at effi¬ 
ciencies given. 


TABLE LXII 


Combined Motor and Pump Efficiency. 


64 60 

Cu. Ft. 338 316 

Lbs.. 21,120 19,800 
Gals.. 2,535 2,370 


56 52 48 

296 275 253 

18,480 17,160 15,840 
2,220 2,062 1,897 


46 43 40 

243 227 211 

15,180 14,190 13,200 
1,822 1,702 1,582 


Combined Motor and Pump Efficiency. 



38 

36 

34 

32 

30 

28 

26 

24 

Cu. Ft. 

200 

190 

180 

169 

158 

148 

137 

127 

Lbs.. 

12,500 

11,880 

11,220 

10,560 

9,900 

9,240 

8,580 

7,920 

Gals. 

1.500 

1,425 

1,350 

1,267 

1,185 

1,110 

1,027 

952 


184 


ELECTRICAL TABLES AND DATA 


TABLE LXII—Continued 


Friction head per hundred feet of pipe of inside 
diameters given. Condensed from Westinghouse 
Electric & Mfg. Co. table. 


Inside Diameters of Pipes. 


Cu. Ft. Lbs. 

Gals. 

%" 

1 " 

1 %" 

i y 2 " 

2 " 


3" 

0.6 

37 

5 

7.59 

1.93 

0.71 

0.27 




1.1 

75 

10 

29.9 

10.26 

2.41 

1.08 




1.6 

112 

15 

66.01 

16.05 

5.47 

2.23 




2.4 

150 

20 

115.92 

28.29 

9.36 

3.81 




3.0 

187 

25 


43.70 

14.72 

5.02 

1.18 



3.4 

225 

30 


63.25 

21.04 

8.62 

2.09 



4.2 

263 

35 


85.10 

28.52 

11.61 

2.76 



4.8 

300 

40 


110.40 

37.03 

14.99 

3.68 

1.19 


5.2 

338 

45 



46.46 

18.74 

4.60 

1.49 


6.0 

375 

50 



57.27 

23.00 

5.61 

1.86 

0.80 

9.0 

562 

75 



129.09 

51.52 

12.23 

4.14 

1.70 

12.0 

750 

100 




89.70 

21.75 

7.36 

3.01 

15.0 

937 

125 





34.27 

11.24 

4.57 

18.0 

1,125 

150 





48.76 

16.10 

6.55 

21.0 

1,312 

175 





64.63 

21.75 

8.85 

24.0 

1,500 

200 





86.25 

28.68 

11.54 

30.0 

1,875 

250 






45.21 

17.84 

36.0 

2,250 

300 






64.53 

25.76 

42.0 

2,625 

350 







34.9,6 

48.0 

3,000 

400 







44.85 

60.0 

3,375 

450 







57.50 

75.0 

3,750 

500 







70.84 


ELECTRICAL TABLES AND DATA 


185 


Table for determining com- Theoretical and practical 
bined efficiency of pump and suction limit, 
motor. 

TABLE LXII—Continued 


Motor 






Altitud'e Theoretical ] 

Practical 

Efficiency 


Pump Efficiency 


Sea level 

33.95 

25 


75 

65 

50 

45 

40 

35 

1,320 ft. above 

32.38 

24 

70 

52 

46 

35 

32 

28 

24 

2,640 ft. above 

30.79 

23 

75 

56 

48 

38 

34 

30 

26 

3,960 ft. above 

29.24 

21 

80 

60 

52 

40 

36 

32 

28 

5,280 ft. above 

27.76 

20 

85 

64 

56 

43 

38 

34 

30 

10,560 ft. above 

22.82 

17 


Reactive Coils. —This term describes coils intro¬ 
duced into a circuit to produce a certain reactance. 
They are also known as reactors. They are used to 
limit short-circuiting currents. Reactors are usually 
designed for a high temperature rise, and should be 
treated as sources of heat. When used in connection 
with lightning arresters they are often spoken of as 
“choke coils .” 

Rectifiers. —The mercury-arc rectifier is the one 
most used for arc lamp operation and is very common 
in motion picture theaters. Other types are the elec¬ 
trolytic and rotary. The mercury-arc type is also 
much used for storage battery work in connection 
with automobile charging. It is usually fed through 
autotransformers, but sometimes through constant 
current transformers, and then delivers a constant 
current. Most rectifiers are operated on single-phase 
circuits, but they can be arranged for two-phase and 
three-phase circuits and operate more advantageously. 
They may also be operated in parallel. Rectifiers de¬ 
signed for 40 to 50 amperes usually have glass tubes, 
but if larger capacities are required, the tubes are 
metallic. The power factor is ordinarily about 0 90. 
The drop in voltage is always about the same, hence 


186 


ELECTRICAL TABLES AND DATA 


the lower the voltage the lower the efficiency. The 
average efficiency is about 75 or 80 per cent. If the 
vacuum is good, shaking the tube will cause a metallic 
sound; if tube is dirty on inside, the vacuum is usually 
poor. 

Reciprocals of Numbers. —The reciprocal of any 
number is equal to 1 divided by that number. The 
reciprocal gives by multiplication what the number 
would give by division, and vice versa. The prin¬ 
ciple involved is made use of in many formulae and 
is much used to facilitate calculations. The recipro¬ 
cals have been given only for whole numbers and up 
to the number 100. The reciprocal of any number 
larger or smaller may, however, easily be found by 
adding a decimal point to the reciprocal for each num¬ 
ber added to its integer or subtracting one for each 
integer taken from the whole number. The larger 
the number, the more decimal places the reciprocal 
will contain. The smaller the number, the greater 
will be its reciprocal. 


Thus the reciprocal of 7.3 0.13698 

73 0.013698 

730 0.0013698 

7300 0.00013698 

0.73 1.3698 

0.073 13.698 


0.0073 136.98 


To find the reciprocal of a number trace along until 
this number is found. Thus the reciprocal of 21.7 
is 0.04608. 

To find the number pertaining to any reciprocal 
find the reciprocal and take the number. Thus the 
whole number of which 0.2710 is the reciprocal is 36.9. 


ELECTRICAL TABLES AND DATA 


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187 


Beciprocals of Numbers 


















188 


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ELECTRICAL TABLES AND DATA 


180 


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190 


ELECTRICAL TABLES AND DATA 


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ELECTRICAL TABLES AND DATA 


191 


Reflectors.—Perfect prismatic glass makes the 
very best reflector. The following table gives approxi¬ 
mately the percentage of light reflected by various 
materials: 


TABLE LXIY 


Well polished silver. 

Silvered mirror. 

Highly polished brass. 

Mirror backed with amalgam. 

Well polished copper. 

Well polished steel. 

Burnished copper. 

Chrome yellow paper. 

Orange paper. 

Yellow paper or painted wall 

Pink paper. 

Blue wall paper. 

Emerald green paper. 

Dark brown paper. 

Vermilion paper. 

Bluish green paper. 

Cobalt blue paper. 

Deep chocolate colored paper 

Black cloth. 

Black velvet. 


Per Cent 
Light 
Reflected 


92 

70 to 90 
70 to 85 
70 

60 to 70 
60 

40 to 50 
60 
50 
40 
35 
25 
18 
13 
12 
12 
12 
4 

1.2 

0.4 


Refrigeration.—Refrigeration by machinery is 
much more reliable, effective and cleanly than that 
produced by the use of ice. Electric power compares 
favorably with steam power in large installations, but 
more especially so in the smaller plants. Its main 
advantages are: lower first cost, less space required; 
less attendance and operation; can be made automatic. 
For direct current, compound-wound motors are pref¬ 
erable, and where variable speed is desired, the speed 
control should be by means of field regulation. For 
alternating current, the squirrel cage type of arma- 






















192 


ELECTRICAL TABLES AND DATA 


ture may be used, but if speed control is desired, a 
wound armature should be provided. The latter is 
much preferable for automatic control. The horse¬ 
power required for refrigeration can be determined 
by means of the curves in Figure 17, due to Westing- 
house Electric & Mfg. Co. The upper curve is for 
compressors of 50 H.P. and smaller; the lower curve 



for larger machines. For example: a 30-ton com¬ 
pressor requires a 52 H.P. motor; a 300-ton com¬ 
pressor requires a 470 H. P. motor. When the ice¬ 
making capacity of compressor is given, the motor 
H. P. required will in general be about double the 
figure given in the curve. 

Refrigerators.—All refrigerators are at times very 
damp. As long as they are kept cold, ice forms, and 
as soon as they are empty the ice melts and all parts 
become wet. No very bright illumination is required, 
and in many of them workmen are required to get 













































































































































































































































































































































































































ELECTRICAL TABLES AND DATA 


193 


along with lanterns. Weatherproof construction is 
preferable to conduit in all places except where heavy 
coatings of ice form on the wires. This frost is scraped 
off from time to time, and open wires are likely to be 
torn loose. Porcelain sockets break easily and should 
not be used. Circuits should not enter or leave too 
close to entrances; the meeting of the cold and warm 
air at such places cause the deposit of much moisture. 
Lamps are usually placed only in runways, and in 
large refrigerators the circuits are apt to be long. In 
some of the large refrigerators watchmen are regu¬ 
larly making rounds; in such places three-way switches 
at doors are useful. Keep cut-outs and switches out¬ 
side of damp rooms and avoid the use of the common 
fiber-lined brass shell socket. 

Residence Wiring. —As a general rule a total 
wattage capacity of about ^ watt per sq. ft. should 
be provided for the whole building, including cellar 
and attic. If these latter are not to be illuminated, 1 
watt per sq. ft. will be ample for the balance of 
house. The best place for service switch and meters 
is in the basement. Select a location easily accessible 
to meter readers. If not too much economy is neces¬ 
sary, let two circuits enter each room that contains 
more than one outlet. Place all switches at doors 
where room is most likely to be entered, and if there 
are two entrances two-way switches will be a great 
convenience. In some elaborate residences circuits 
are sometimes so arranged that lights in all rooms 
may be thrown on by a master switch, even if turned 
off in rooms. This is useful as burglar protection 
and also in case of fires. A measure of protection 
against intruders can be obtained by placing lights 
above doors so that an intruder must show himself 
in the light before he can enter a room. The bright 
light will prevent him from seeing what is inside 
the door. 


194 


ELECTRICAL TABLES AND DATA 


Attics .—No part of residence requires light more 
than the attic. The use of matches is exceedingly 
dangerous in such places. Run wires where they will 
not be molested. 

Bathroom .—A center light in a bathroom is an 
abomination. Place a light at each side of shaving 
mirror if practicable, but locate them so that person 
in tub cannot reach socket. An outlet for heater will 
be a great convenience. If possible place or shade 
lamps so they will not cast shadows of persons on 
window. Place a switch at door. If expense is no 
object, inverted lighting will be very useful. 

Basement .—The wiring of the basement depends 
upon the use to which it may be put. Two or three- 
way switches, one at each entrance, will be very con¬ 
venient. Plenty of light will be an inducement for 
servants to keep basement cleaner than the average. 
Provisions should be made for motors to operate ice 
cream freezers, washing machines, mangels, or vacuum 
cleaning motors. It is much preferable to place the 
motor for this purpose in the basement rather than to 
bother with portable machines. Fan motor outlets 
will assist in drying clothes. If part of basement is 
used as laundry and likely to be damp, use weather¬ 
proof construction and avoid placing sockets where 
one standing on wet floor will be likely to touch them. 
Provide outlet for flatiron. 

Bedrooms .—A center fixture should never be in¬ 
stalled in a bedroom unless it is intended also as a sort 
of living room. Lights should be arranged to suit 
the various positions in which a bed can advantage¬ 
ously be placed, and so that one can use the light for 
reading in bed or make easy connections for heating 
pads. Special outlets along baseboard for flatiron 
heaters, sewing machine motors, etc., will be found 
very useful. One light on each side of dresser mirror 
is a great convenience. Avoid placing lights so that 


ELECTRICAL TABLES AND DATA 


195 


they will cast shadows of occupants on windows. For 
protection against burglars, a switch by which lights 
in other rooms may be turned on is very effectual. 
See “Modern Wiring Diagrams and Descriptions” 
for circuits. Such a switch might be placed in each 
bedroom. Inverted lighting is very useful if only one 
light can be installed and if ceilings are light enough. 

Cellars .—A cellar is usually damp, and weather¬ 
proof construction should be used. Keep switch out¬ 
side at door. 

Closets .—The use of matches in closets is very dan¬ 
gerous and will be entirely eliminated by good illum¬ 
ination. Place a light at ceiling and control by switch 
if closet is small. In large closets a pendant light may 
be advisable, but there is usually too much chance of 
clothing coming in contact with it and the cord. 

Dining Rooms .—Beam lighting is used to some ex¬ 
tent in dining rooms. Special illumination of buffet 
and china closet is also often practiced. Small lamps 
are used for the latter and should be located to show 
off cut glass, etc., to the best advantage. It is well 
to study the effect of such lights carefully before 
finally locating them. To show T off silverware, fine 
table linen, etc., to the best advantage it is advisable 
to concentrate a strong light upon the table and 
leave balance of room somewhat dark. Side outlets 
for fan motors, and floor sockets for chafing dishes, 
are very useful. The low hanging fixtures often seen 
in dining rooms should not be recommended. They 
will soon become obnoxious. 

Halls .—Halls ordinarily require only a perfunc¬ 
tory illumination unless a showy appearance is de¬ 
sired. These lights are often combined with stair 
lights and fitted with two or three-way switches. 
Place switch for hall light close to the door. 

Ice Boxes or Chambers .—A light placed opposite 
door will be very useful. 


196 


ELECTRICAL TABLES AND DATA 


Kitchen .—If kitchen walls are of light color, a cen¬ 
ter light will give good illumination. With dark col¬ 
ored walls a light should be placed over sink and near 
range, but a little to one side, so as to avoid the cook¬ 
ing fumes as much as possible. A small motor to 
drive steam out will be of great use. Ozonators to 
destroy odors will also be much appreciated. As 
ironing is often done in the kitchen, an outlet for 
irons should always be provided. If electric cooking 
is indulged in this must be provided for. 

Laundry .—There should be a light directly over 
wash tubs and another arranged to be directly over 
ironing board. If clothes are dried in laundry a fan 
or ventilating motor will be of great service. Pro¬ 
visions should be made for washing machine motors, 
mangels and flatiron. Locate sockets so persons will 
not be likely to touch them while standing on wet 
floor. 

Lavatory .—One light controlled by door-switch is 
very useful here. 

Library .—Inverted lighting of sufficient c. p. to 
allow the reading of titles of books in cases is the best 
means of illumination here. In addition to this there 
should be outlets for reading lamps and brackets con¬ 
veniently located on walls to give a brighter light for 
those that need it. A direct light with strong reflector 
under inverted light is useful for reading purposes. 

Nursery .—The lighting of the nursery should be 
ample, but precautions should be taken to guard 
against the possibility of outlets being short circuited 
by children. Avoid placing sockets within easy reach. 
Electric toys should be confined to battery current, 
or a low-voltage transformer, to which children have 
no access, might be used. The lighting voltage is too 
dangerous for them. Control all lights by switches 
and keep them high. 


ELECTRICAL TABLES AND DATA 


197 


Pantry. —Provide bright illumination to show up 
dust and dirt and induce cleanliness. 

Parlor. —The illumination of the parlor is usually 
effected by means of quite elaborate chandeliers. Out¬ 
lets for piano and reading lamps should be provided. 
The center light does not illuminate pictures very 
well, and for this reason inverted lighting is often 
useful. Really good pictures, however, deserve spe¬ 
cial illumination. 

Porch. —A light should be arranged close to main 
entrance and so located as to reveal features of per¬ 
sons applying for admission without making the 
party inside of house visible. The light should be 
controlled by a switch inside and should be out of 
reach from the outside. If porch is to be enclosed, 
other outlets-for lamps or fan motors will be useful, 
but they should be arranged at ceiling so as to avoid 
moisture. Use no fiber lined sockets outside. 

Resuscitation from Electric Shock. —Rules recom¬ 
mended by commission on resuscitation from electric 
shock, representing The American Medical Associa¬ 
tion, The National Electric Light Association, The 
American Institute of Electrical Engineers. Issued 
and copyrighted by National Electric Light Associa¬ 
tion. Reprinted by permission. 

Follow these instructions even if victim appears 
dead. 

I. Immediately Break the Circuit. —With a single 
quick motion, free the victim from the current. Use 
any dry non-conductor (clothing, rope, board) to 
move either the victim or the wire. Beware of using 
metal or any moist material. While freeing the vic¬ 
tim from the live conductor have every effort also 
made to shut off the current quickly. 

II. Instantly Attend to the Victim’s Breathing .— 
(1) As soon as the victim is clear of the conductor, 
rapidly feel with your finger in his mouth and throat 


198 


ELECTRICAL TABLES AND DATA 


and remove any foreign body (tobacco, false teeth, 
etc.). Then begin artificial respiration at once. Do 
not stop to loosen the victim’s clothing now; every 
moment of delay is serious. Proceed as follows: 

a. Lay the subject on his belly, with arms extended 
as straightforward as possible and with face to one 
side, so that nose and mouth are free for breathing. 



Figure 18. Inspiration—Pressure Off. 


See Figure 18. Let an assistant draw forward the 
subject’s tongue. 

b. Kneel straddling the subject’s thighs and facing 
his head; rest the palms of your hands on the loins 
(on the muscles of the small of the back), with fingers 
spread over the lowest ribs, as in Figure 18. 

c. With arms held straight, swing forward slowly 
so that the weight of your body is gradually, but not 
violently, brought to bear upon the subject. See Fig¬ 
ure 19. This act should take from two to three 
seconds. 

Immediately swing backward so as to remove the 







ELECTRICAL TABLES AND DATA 


199 


pressure, thus returning to the position shown in 
Figure 18. 

d. Repeat deliberately twelve to fifteen times a min¬ 
ute the swinging forward and back—a complete res¬ 
piration in four or five seconds. 

e. As soon as this artificial respiration has been 
started, and while it is being continued, an assistant 



Figure 19. Expiration—Pressure On. 


should loosen any tight clothing about the subject’s 
neck, chest or waist. 

(2) Continue the artificial respiration (if neces¬ 
sary, at least an hour), without interruption, until 
natural breathing is restored, or until a physician 
arrives. If natural breathing stops after being re¬ 
stored, use artificial respiration again. 

(3) Do not give any liquid by mouth until the sub¬ 
ject is fully conscious. 

(4) Give the subject fresh air, but keep him warm. 

III. Send, for Nearest Doctor as Soon as Accident 

Is Discovered. 





200 


ELECTRICAL TABLES AND DATA 


Ropes.— 


. TABLE LXV 

Standard Iron Hoisting Rope, 6 Strands—19 Wires to the 
Strand—1 Hemp Rope. American Steel & Wire Co. 


Diameter 
in Inches 

Circumference 
in Inches 

Approximate 
Weight Per Ft. 
in Founds 

Approximate 
Strength in Tons 
of 2,000 Lbs. 

Proper Working 
Load in Tons 

Diameter of 
Drum or Sheave 
Advised in Feet 

2| 

8! 

11.95 

111.0 

22.2 

17 

2* 

7f 

9.85 

92.0 

18.4 

15 

21 

7* 

8.00 

72.0 

14.4 

14 

2 

6f 

6.30 

55.0 

11.0 

12 

If 

5f 

5.55 

50.0 

10.0 

12 

If 

5J 

4.85 

44.0 

8.8 

11 

If 

5 

4.15 

38.0 

7.6 

10 

If 

4f 

3.55 

33.0 

6.6 

9 

If 

4f 

3.00 

28.0 

5.6 

8.5 

If 

4 

2.45 

22.8 

4.56 

7.5 

If 

3f 

. 2.00 

18.6 

3.72 

7.0 

1 

3 

1.58 

14.5 

2.90 

6.0 

f 

2f 

1.20 

11.8 

2.36 

5.5 

f 

2f 

0.89 

8.5 

1.70 

4.5 

f 

2 

0.62 

6.0 

1.20 

4.0 


If 

0.50 

4.7 

0.94 

3.5 

f 

If 

0.39 

3.9 

0.78 

3.0 

15 

If 

0.30 

2.9 

0.58 

2.75 

f 

If 

0.22 

2.4 

0.48 

2.25 


I 

0.15 

1.5 

0.30 

2.00 

1 

f 

0.10 

1.1 

0.22 

1.50 


For better grades of rope smaller sheaves are 
advised. 


ELECTRICAL TABLES AND DATA 


201 


Manila Kope. 


9h 

o> 

•4-^ 

o> 

© 

Vi 

© 

£ 

<D rj 

-K £ 

-v> 
c a 2 

TS r ° 

© 

■v> 

© 

© 

Vi 

© 

«4H 

£ 

© rl 

f tS> 

m 2 
rrl O 

s 

p 

© 

Vt 

8 0 
• rH (U 

a P 

P v. 

6 

0 

© 

3 g 

H-> L- 

SP 

3 v. 

• rH 

P 

• H 

O 

P 02 

o <u 

pp 

• iH 

P 

• pH 

Q 

C 

P CG 

o © 

pp 

1 

U 

2,000 

0.09 

If 

4* 

13,500 

0.65 

f 

2 

3,250 

0.14 

u 

41 

15,000 

0.77 

i 

2i 

4,000 

0.20 

If 

4f 

18,200 

0.90 

I 

2# 

6,000 

0.27 

If 

51 

21,700 

1.05 

l 

3 

7,000 

0.35 

2 

6 

25,000 

1.40 

U 

3$ 

9,300 

0.45 

21 

61 

32,000 

1.75 

H 

3* 

10,000 

0.55 

2 1 

71 

40,000 

2.15 


Splicing of Manila Rope .—The successive opera¬ 
tions for making a common or English splice in a 
lj-inch 4-strand rope is as follows: 

1. Tie a piece of twine, 9 and 10, A, Figure 20, 
around the rope to be spliced, about six feet from 
each end. Then unlay the strands of each end back to 
the twine. 

2. Put the ropes together and twist each corre¬ 
sponding pair of strands loosely, to keep them from 
being tangled, as shown at A. 

3. The twine 10 is now cut, and the strand 8 unlaid 
and strand 7 carefully laid in its place for a distance 
of four and a half feet from the junction. 

4. The strand 6 is next unlaid about one and a half 
feet and strand 5 laid in its place. 

5. The ends of the cores are now cut off so they 
just meet. 

6. Unlay strand 1 four and a half feet, laying 
strand 2 in its place. 

7. Unlay strand 3 one and a half feet, laying in 
strand 4. 


202 


ELECTRICAL TABLES AND DATA 


8. Cut all the strands off to a length of about 
twenty inches, for convenience in manipulation. The 
rope now assumes the form shown in B, with the 
meeting point of the strands three feet apart. 

Each pair of strands is now successively subjected 
to the following operations: 


Figure 20.—Method of Splicing Ropes. 



9. From the point of meeting of the strands 8 and 
7 unlay each one three turns; split both the strand 8 
and the strand 7 in halves, as far back as they are 
now unlaid, and the end of each half strand 
* ‘whipped” with a small piece of twine. 

10. The half of the strand 7 is now laid in three 
turns, and the half of 8 also laid in three turns. The 
half strands now meet and are tied in a simple 











ELECTRICAL TABLES AND DATA 


203 


knot 11, C, making the rope at this point its original 
size. 

11. The rope is now opened with a marlinspike, 
and the half strand of 7 worked around the half 




Figure 21.—Methods of Tieing Knots. 


strand of 8 by passing the end of the half strand 
through the rope, as shown, drawn taut, and again 
worked around this half strand until it reaches the 
half strand 13 that was not laid in. This half strand 
13 is now split, and the half strand 7 drawn through 
the opening thus made, and then tucked under the 
two adjacent strands, as shown in D. 


































204 ELECTRICAL TABLES AND DATA 

12. The other half of the strand 8 is now wound 
around the other half strand 7 in the same way. 
After each pair of strands has been treated in this 
manner, the ends are cut off at 12, leaving them 
about four inches long. After a few days’ wear they 
will draw into the body of the rope or wear off, so 
that the locality of the splice can scarcely be detected. 

Figure 21 shows specimens of knots frequently 
used. 

A, Bowline; B, Stevedore knot; C, Beef knot; D. Weavers 
knot; E, Boat knot; F, Half hitch; G, Timber hitch; H, Clove 
hitch; I , Timber and half hitch; J, Blackwall hitch; E, Common 
noose; L, Fishermen’s bend; M, Common knot; N, Turks head. 

Saloons. —In small saloons not much illumination 
is required. Where there is any pretense of impor¬ 
tance, however, there is always some back-bar lighting, 
and this may often furnish the whole illumination. 
Special outlets for cash registers and hot water heat¬ 
ers should be provided. Nearly every saloon sooner 
or later provides a beer pump. In pretentious saloons 
a very elaborate illumination is often striven for. 
In case wine rooms, or other private places fitted with 
glass partitions, are to be illuminated the lights should 
be so placed that they will not cast shadows of occu¬ 
pants on glass. 

Schools. —In large cities schools are often classed 
as assembly halls and special rules for wiring are 
made. There should be emergency lighting. A stere- 
opticon outlet is a common requirement. 

Screws. —Formulae for wood screws. N = number; 
D = diameter. 


D= (Nx 0.01325) + 0.056 
„ D- 0.056 



ELECTRICAL TABLES AND DATA 


Ms 


TABLE LXYI 


Dimensions of Iron Screws (Approximate). 


Trade 

Diameter 

Nearest 

Greatest Length 

Number 

in Fractions 

B. & S. Gauge 

Obtainable 

0 

%28 

15 

% 

1 

%28 

14 

% 

2 

%4 

12 

% 

3 

%2 

11 

1% 

4 

7 /&4 

9 


5 

%2 

8 

2 y 2 

6 

17 / i 28 

7 

3 

7 

J %28 

7 

3 

8 

%2 

6 

4 

9 

n /64 

5 

4 

10 

*%4 

5 

4 

11 

13 /64 

4 

4 

12 

27 A 28 

4 

6 

13 

2 %28 

3 

6 

14 

15 /64 

3 

6 

15 


2 

6 

16 

17 /64 

2 

6 

17 

%2 

1 

6 

18 

*%4 

1 

6 

Service 

Entrance. — The 

service wires should be 


protected by fuses as close as possible to where they 
enter the building. There shoidd be a service switch, 
and it and the fuses should be accessible. 

Shelving. —To illuminate shelving properly is a 
troublesome matter. Portable lamps are essential, 
but these introduce an appreciable fire hazard. It is 
best to suspend lamps from ceiling by reinforced cord, 
and fit each lamp with a substantial guard. It is 
usually necessary to have good light close to the floor, 
but this can be had by keeping lamps about 6| foot 
above floor. If shelves are deep and contain dark- 


206 


ELECTRICAL TABLES AND DATA 


colored materials carrying indistinct numbers, attach¬ 
ments to these cords will often be necessary. Where 
lights are not constantly in use, three-way ceiling 
switches will be very useful and economical. Provide 
each group of lamps commonly used together with its 
own switch. 

Show Windows. —In the best form of show-window 
lighting the lamps are always entirely hidden. Very 
brilliant effects are often striven for and the gas- 
filled mazda lamp is in great favor. Where there is 
bright illumination on the street in front, even greater 
illumination is required within. The object is, not 
only to make things visible, but to attract attention, 
and for this purpose the very brightest and whitest 
light is necessary. Most show windows are lighted 
from the top by reflectors, but in some cases an illum¬ 
ination from the bottom up must also be provided. In 
some cases the object is to show the lights and call 
attention to the fact that they are there. For this 
purpose small lamps, Well frosted, are preferable. If 
they are too bright they will blind people to the ob¬ 
jects in window. In some cases 32 c. p. lamps have 
been thickly studded over the whole ceiling of window. 
Time switches are much used for show-window light¬ 
ing and enable one to keep his windows illuminated 
for advertising purposes after the store is closed. 
Fan motor outlets are very useful for winter to keep 
windows clear of frost. Place no wires near glass 
where water is liable to run down. 

Signs, Electric.—Signs should be wired with the 
two sides .independent so as to enable flasher to be 
used. Small lamps of low intrinsic brilliancy are 
preferable. Letters should be glossy white and kept 
clean. The following table gives dimensions and 
numbers of sockets of stock letters made by the Fed¬ 
eral Electric Co. of Chicago, which may serve as a 
general guide to present practice. 


ELECTRICAL TABLES AND DATA 


207 


TABLE LXYII 



10 Inch 
Letters 

14 Inch 
Letters 

16 Inch 
Letters 

4 Lamp High 

16 Inch 
Letters 

5 Lamp High 

24 Inch 
Letters 


Sockets 

Width 

Sockets 

Width 

Sockets 

Width 

Sockets 

Width 

Sockets 

Width 

1 

A 

8 

10 

8 

12 % 

8 

15i/ 2 

10 

15/2 

11 

21 

B 

10 

10 

10 

12 % 

11 

15/2 

13 

151/2 

13 

21 

C 

r*» 

4 

10 

7 

12 % 

7 

15/, 

8 

151/2 

8 

21 

D 

8 

10 

8 

12 % 

9 

15/2 

11 

15/2 

11 

21 

E 

9 

10 

9 

12 % 

9 

15/2 

10 

15/2 

13 

21 

E 

7 

10 

7 

12 % 

7 

151/2 

8 

15/2 

10 

21 

G 

8 

10 

8 

12 % 

8 

15/2 

9 

15/2 

11 

21 

H 

9 

10 

9 

12 % 

9 

15/2 

11 

15/2 

12 

21 

I 

4 

5% 

4 

6 

4 

8 

5 

8 

5 

9 

J 

6 

10 

6 

12 % 

6 

1514 

7 

15/2 

7 

21 

K 

8 

10 

8 

12 % 

9 

IS/, 

11 

15/2 

11 

21 

L 

6 

10 

6 

12 % 

6 

151/2 

7 

15/2 

8 

21 

M 

13 

12 % 

13 

15 % 

13 

19/2 

15 

19/2 

17 

25 

N 

10 

10 

10 

15 % 

10 

15/2 

13 

15/2 

13 

21 

O 

8 

10 

8 

15 % 

9 

15/2 

10 

15/2 

10 

21 

P 

8 

10 

8 

15 % 

8 

15H 

10 

15/2 

10 

2 L 

Q 

9 

10 

10 

15 % 

9 

l5i/ 2 

10 

151/2 

11 

21 

R 

10 

10 

10 

15 % 

10 

15/2 

12 

151/2 

12 

2 L 

s 

8 

10 

8 

15 % 

8 

151/2 

10 

15/2 

10 

21 

T 

6 

10 

6 

15 % 

6 

15/2 

7 

15i/ 2 

8 

21 

II 

8 

10 

8 

15 % 

9 

15/2 

10 

15/2 

10 

21 

V 

7 

10 

7 

15H 

7 

15/2 

9 

15/2 

9 

21 

IV 

12 

12 1 /, 

12 

15 % 

13 

19/2 

15 

191/ 

15 

25 

X 

8 

10 

8 

15 % 

9 

15/2 

9 

151/2 

9 

21 

Y 

6 

10 

6 

15 % 

6 

15/2 

7 

15/2 

8 

21 

z 

8 

10 

8 

15 % 

8 

15/2 

9 

151/2 

11 

21 

& 

8 

10 

8 

15 % 

9 

IS/, 

9 

15/2 

10 

21 

1 

4 

10 

4 

15 % 

4 

15/2 



6 

21 

2 

9 

10 

8 

15 % 

8 

15/2 



11 

21 

3 

9 

10 

7 

15 % 

7 

15/2 



9 

21 

4 

7 

10 

7 

15 % 

7 

151/2 



11 

21 

6 

10 

10 

10 

15 % 

10 

15/2 



J 2 

21 

6 

9 

10 

8 

15 % 

9 

15/2 



11 

21 

7 

6 

10 

6 

15 % 

6 

15/2 



8 

21 

8 

11 

10 

11 

15 % 

8 

151/2 



10 

21 

9 

9 

10 

8 

15 % 

9 

15/2 



11 

21 

$ 

8 

10 

8 

15 % 

8 

15/2 



8 

21 





15 % 


15/2 






The supporting cable is usually attached to the 
electric sign somewhat back of its outer end, and it 
may be assumed that the cable carries about 60 per 
cent of the weight of sign. With this assumption and 




































208 


ELECTRICAL TABLES AND DATA 


using a safety factor of 5, the strength of the cables 
necessary to support it can be found by the formula: 


$ = 5 x .60 x W 


VH 2 + D 2 

II 


where W - weight of sign; II = height of attachment 
to wall above sign, and D = the distance from attach¬ 
ment on sign to a point vertically under sign support. 

Table LXVIII is calculated according to this for¬ 
mula (omitting W), and to find the proper cable to 
support a given sign it is but necessary to multiply 
number found at intersection of line pertaining to 
height of support and that pertaining to distance of 
sign attachment from wall, by the weight of sign. 
The result will give the breaking strain of the neces¬ 
sary cable. 


TABLE LXVIII 


Supports for Weight of Sign. 

Distance 
from Wall to 


Attachment on 
Sign in Feet 


Height of 

Cable 

Fastening 

Above Sign in 

Feet 


3 

4 

5 

6 

8 

10 

12 

14 

16 

18 

20 

4 

5 

4 

4 

3.6 

3.4 

3.2 

3.0 

3 

3 

3 

3 

5 

6 

5 

4.2 

3.7 

3.5 

3.3 

3.2 

3 

3 

3 

3 

6 

7 

5.4 

5.0 

4.2 

3.8 

3.5 

3.4 

3.2 

3 

3 

3 

7 

8 

6.0 

5.1 

4.7 

4.0 

3.7 

3.5 

3.4 

3.3 

3 

3 

8 

8.6 

6.8 

5.7 

5.0 

4.2 

4.0 

3.6 

3.5 

3.4 

3.3 

3 

10 

10.5 

8.1 

6.9 

6.0 

5.0 

4.4 

3.9 

3.8 

3.6 

3.4 

3.3 

12 

12.4 

9.4 

7.8 

6.7 

5.4 

4.6 

4.3 

4.0 

3.7 

3.5 

3.4 

14 

14.6 

11.1 

9.0 

7.8 

6.0 

5.2 

4.8 

4.1 

4.0 

3.9 

3.7 


SIDE GUYS FOR SIGNS 

The wind pressure on the ordinary sign must be 
calculated on the basis of 20 lbs. per square foot and 
requires much better supports to withstand it than 
are necessary to support the weight of sign, although, 
they are never so provided. 




ELECTRICAL T-.LLLS AXD DATA 


209 


The table below Las been calculated according to the 
same general formula as the one above. To find the 
proper size of cable for side guys, multiply the num¬ 
ber of square feet in sign by number found where 
lines pertaining to the two fastenings of side guys 
cross. 


TABLE LXIX 


Distance of 

Attachment on Distance of Guy Attachment on Wall from 
Sign from Wall Sign in Feet. 



3 

4 

5 

6 

7 

8 

10 

12 

14 

16 

2 

17 

17 

16 

15 

15 

14 

14 

14 

14 

14 

3 

21 

18 

18 

17 

16 

15 

14 

14 

14 

14 

4 

24 

20 

18 

17 

16 

16 

15 

15 

14 

14 

5 

27 

22 

20 

19 

18 

17 

16 

16 

15 

14 

6 

31 

25 

22 

20 

19 

-18 

17 

16 

15 

15 

7 

34 

28 

24 

22 

20 

19 

18 

17 

16 

15 

8 

38 

32 

27 

24 

21 

19 

18 

17 

17 

16 

9 

44 

35 

29 

26 

22 

21 

19 

18 

18 

17 

10 

48 

38 

32 

28 

24 

23 

20 

19 

18 

17 

12 

57 

45 

37 

33 

27 

25 

22 

21 

19 

18 

For signs 

hung 

at 

comers 

the 

distance 

of guy 


attachment on wall must be taken as the point at 
right angles to sign where the guy would strike wall 
if it were at right angles to sign. 


TABLE LXX 


Table showing approximate strength in pounds of 


Standard 

Steel Strand— 

-American Steel & Wire Co. 

Diameter 

Approximate 

Diameter 

Approximate 

in Inches 

Strength 

in Inches 

Strength 


8,500 lbs. 

A 

1,800 lbs. 

rj 

6,500 lbs. 

A 

1,400 lbs. 

3 

fi 

5,000 lbs. 


900 lbs. 

A 

3,800 lbs. 


500 lbs. 


2,300 lbs. 

* 

400 lbs. 


210 


ELECTRICAL TABLES AND DATA 


Cable Supports for Signs Over Streets .—Signs of 
this kind are usually supported from steel cables swung 
across street, or other open place, from the tops of 
buildings or suitable poles. The table below gives the 
stresses caused by various loads per foot evenly dis¬ 
tributed, and also for loads suspended from center. 
The arrangement of sign is usually such that neither 
case exactly applies, so that an approximate mean of 
the two must be taken. The calculations are for a 
100-foot span and a sag of 4 feet. 


TABLE LXXI 


Diam¬ 

eter 

of 

wt. 

per 

Approxi- 

imate 

Stress 
Caused by 
Cable 

Distributed Load 

Load in Center 

Cable 

Foot 

Strength 

Alone 

Pounds Stress 

Pounds 

Stress 

n 

4.85 

84,000 

1,500 

50 

17,140 

2,500 

15,625 

n 

3.55 

60,000 

1,109 

30 

10,484 

7,015 

1,500 

9,375 

li 

2.45 

46,000 

766 

20 

1,000 

6,250 

1 

1.58 

28,000 

22,200 

493 

15 

5,181 

750 

4,687 

1 

1.20 

375 

12 

4,125 

3,090 

600 

3,750 

t 

0.89 

15,600 

278 

9 

500 

3,125 


The above figures represent the maximum loads 
which should be suspended by such cables unless a 
greater sag is allowed, and do not take wind pressure 
into consideration. See “Side Guys .” 

The above figures are based on the following for¬ 
mulae used by American Steel and Wire Co.: 

Wl 2 

giving stress for evenly distributed load, and 
Wl 

S 2 =-rr for stress due to load in center. 

S = stress on cable 

W = weight per foot of cable and load if evenly dis¬ 
tributed, or load in center 
1 = length of span 
<2= sag in feet. 




ELECTRICAL TABLES AND DATA 


211 


To find total stress those due to cable and load must 
be added. 

Slide Rule. —Figure 22 is an illustration of the 
ordinary slide rule. The numbers on the top, or A, 
scale, may be read naturally as 1, 2, 3, 4, etc., ending 
with the last figure 1 at the right, which would then be 
called 100, or these values may be considered in¬ 
creased or decreased to any extent by adding or 
prefixing the necessary number of ciphers. Thus if 
the 2 is called 20 or 200 the 3 would be called 30 or 
300, etc. The same also holds true of the upper half 
of the slide, or B scale. The divisions between the 
main figures are of various dimensions, but serve only 



Figure 22.—The Slide Rule. 


to designate fractional values of the figures. The 
principle of operation can easiest be made clear by 
examples. 

Multiplication .—Set the 1 on upper half of slide 
under one of the factors on scale A. Find the other 
factor on the slide and directly above it you have the 
product. Multiply 4 by 2. Setting the slide as 
directed we find 8. This same setting might be used 
to multiply 40 by 20, or 4000 by 2 or 200. We have 
but to note as we go along by how much we increased 
the value of either of the factors, and add the cor¬ 
responding number of ciphers. Different settings 
could also be used for the same problem. Consid¬ 
erable practice is necessary before one can become 
really proficient in these calculations. 

Division ,—In division the above process is reversed. 
Place the divisor on the slide under the dividend on 












212 


ELECTRICAL TABLES AND DATA 


scale A and the 1 on slide will be directly below the 
quotient. 

Multiplication ancl Division Combined .— 

t, , 7x3x4 

Example: —g-- 

Set 1 on slide under 7, note product above 3; next 
set 1 on slide under this product and note product 
above 4. Now move slide back until 6 is under last 
product and find answer above 1. 

Proportion. —By setting any number on B against 
any convenient number on A it can be seen that all 
other coinciding numbers are in the same proportion 
to each other. Hence any problem in direct propor¬ 
tion can be solved by simply setting the first term on 
B against the second on A; this being done, we shall 
find the last term directly above the third on B. 
Example: If 7 bushels of wheat cost $13.00, how 
much will 23 bushels cost? Answer, $42.71. In 
direct proportion all factors are either increasing or 
decreasing. If they are mixed it is termed Inverse 
Proportion. In order to solve a problem in inverse 
proportion we invert the slide, but continue to read 
A and B together. Example: If 9 men can do a 
piece of Work in 17 days, how many days will 13 
men require? Inverting the slide and setting the 9 
on the left under 17 and bringing the runner over the 
13 at the right at about the center of the scale, we find 
11.8 as the answer. 

Squaring Numbers and Extracting Square Boots .— 
When the slide is set even on all sides, the numbers 
in the scales A and B are the squares of those in 
C and D. Hence also those in the last named scales 
are the square roots of the upper. They must, how¬ 
ever, be taken with the proper number of ciphers. 
The square of 2, for instance, is 4, that of 20 is 400 



ELECTRICAL TABLES AND DATA 


213 


and that of 200 equals 40,000. In extracting square 
roots, if the number of digits is odd, 4, 400, etc., the 
root will be found directly under the number on left 
hand side of scale. If the number of digits is even, 
it will be found on right hand side, viz., square root 
of 40 equals 6.41. 

Extracting Cube Root .—Set the runner on the 
number, the root of which is to be found, and shift the 
slide until the same number found under this num¬ 
ber is also found under the index of the slide on the 
lower part D. According to location of runner either 
the right or left hand index must be used. Practice 
raising number to the third power; reversing this 
process will show method of extracting roots. 

Sockets. —Nearly all lamps used in this country 
are fitted with the well-known Edison base. A few 
old installations equipped with the T. H. base still 
remain, but are usually equipped with adjusters to 
permit the use of Edison base lamps. 

The standard sockets as recognized by the N. E. C. 
are given below: 

Classification .—Sockets to be classed according to 
diameters of lamp bases, as Candelabra, Medium and 
Mogul. Base to be known respectively as ^ inch, 
1 inch and 1J inch nominal sizes, with ratings as 
specified in the following table: 




-Ratings 


V 


Key 


Keyless 

Max. 


Max. 





Amp. 



Amp. 



at any 



at any 


Nominal 

Volt- 



Volt- 

Class 

Diam. Watts Volts 

age 

Watts 

Volts 

age 

Candelabra i in. 75 125 

t 

75 

125 

1 

Medium 

1 “ 250 250 

2i 

660 

250 

6 

Mogul 

(a)660 250 

li in. 

6 

660 

1,500 

600 

250 



(b) 


1,500 

600 





214 


ELECTRICAL TABLES AND DATA 


(a) This rating may be given only to sockets having a 
switch mechanism which produces both a quick “make” and 
a quick ‘‘break” action. 

(b) Ratings to be assigned later, pending further discus¬ 
sion with manufacturers. 

Miniature sockets and receptacles having screw 
shells smaller than the candelabra size may be used 
for decorative lighting systems, Christmas tree light¬ 
ing outfits, and similar purposes. 

Double-ended Sockets .—Each lamp holder to be 
rated as specified above, the device being marked with 
a single marking applying to each end. 

In addition to these there is the Edi-Swan base, 
which is § inch diameter, and has bayonet-type con¬ 
nections and is sometimes used on automobiles and 
other places where there is much jarring. The Edison 
miniature base is f inch in diameter and is used only 
for low voltages. Some very small lamps are made 
without bases, the wires connecting direct to lamp 
terminals. The mogul socket is used for series in¬ 
candescent lighting and often fitted with automatic 
cut-out. It is also used for gas-filled lamps of 300 
watts or over. Fiber lined or brass shell sockets 
should not be used in damp places, or where corrosive 
vapors exist. Key sockets should also be avoided in 
damp places, or where inflammable gases may exist. 

Sparking Distances. —Very high-test voltages are 
often measured by their sparking distance. The fol¬ 
lowing table gives the sparking distances between 
sharp points corresponding to different alternating 
current voltages, when the ratio between maximum 
and mean effective voltages is equal to 1.41, or the 
square root of two. The values given were derived 
from a long series of careful and accurate tests. 


ELECTRICAL TABLES AND DATA 


215 


TABLE LXXII 


(Copyright, 1906, by Standard Underground Cable Co.) 


Volts 

Spark 


Spark 


Spark 

Distance 

Volts 

—Distance— 

Volts 

—Distance— 


A. or B. 


A. 

B. 


A. 

B. 

1,000 

0.028 

18,000 

0.945 

0.945 

35,000 

1.840 

1.895 

2,000 

0.098 

19,000 

0.995 

0.995 

36,000 

1.900 

1.958 

3,000 

0.159 

20,000 

1.042 

1.042 

37,000 

1.945 

2.020 

4,000 

0.216 

21,000 

1.092 

1.097 

38,000 

2.012 

2.085 

5,000 

0.270 

22,000 

1.143 

1.150 

39,000 

2.062 

2.153 

6,000 

0.324 

23,000 

1.195 

1.206 

40,000 

2.127 

2.220 

7,000 

0.378 

24,000 

1.247 

1.260 

41,000 

2.190 

2.290 

8,000 

0.432 

25,000 

1.300 

1.314 

42,000 

2.247 

2.360 

9,000 

0.487 

26,000 

1.353 

1.373 

43,000 

2.308 

2.434 

10,000 

0.540 

27,000 

1.405 

1.427 

44,000 

2.370 

2.506 

11,000 

0.595 

28,000 

1.460 

1.485 

45,000 

2.432 

2.580 

12,000 

0.644 

29,000 

1.512 

1.540 

46,000 

2.495 

2.660 

13,000 

0.695 

30,000 

1.566 

1.600 

47,000 

2.560 


14,000 

0,746 

31,000 

1.620 

1.655 

48,000 

2.625 


15,000 

0.797 

32,000 

1.675 

1.712 

49,000 

2.692 


16,000 

0.845 

33,000 

1.728 

1.772 

50,000 

2.760 


17,000 

0.897 

34,000 

1.785 

1.833 

s' 





SPARKING DISTANCES IN INCHES. 


Column A gives spark distances with 10 inch con¬ 
cave metal shields, the plane of whose edges was 1 inch 
back of the needle points. Column B gives the spark 
distances without shields. 

Sharp needles are essential for uniform spark dis¬ 
tances, as points measuring from 0.001 inch to 0.002 
inch gave in many instances spark distances that 
were from 20 to 45 per cent greater than those ob¬ 
tained with sharp points. See also table of A. I. E. E. 
in Standardization Recommendations. 

Specific Gravity (Solids). —The specific gravity of 
a substance is defined as the ratio of the weight of that 
substance to the weight of an equal volume of water 
or air. Water is used as the standard of liquids and 
solids. Air at the temperature 0°, C. (32° F.) and 
766 mm. mercury pressure for gases. By multiplying 
the specific gravity of any substance by the weight 


216 


ELECTRICAL TABLES AND DATA 


of an equal volume of water we find the weight of 
that volume of the material. The weight of a cubic 
foot of water is approximately 62.5 lbs. The weight 
of a gallon is approximately 8.33 lbs. To find the 
specific gravity of a body heavier than water approx¬ 
imately by experiment, weigh it in air and then weigh 
it in pure water. Divide the weight in air by the 
loss of weight (buoyancy) in water and the quotient 
will give the specific gravity. If the body is lighter 
than water load it down with a substance heavy 
enough to sink it. Then weigh the two submerged 
together. Also weigh both separately in air and the 
heavy body in water. Subtract the buoyancy of the 
heavy body from the buoyancy of the two bodies to¬ 
gether. The remainder will be the buoyancy of the 
lighter body by which its weight in air is to be divided 
as before. 

Specifications.—In many cases preliminary specifi¬ 
cations, setting forth what the purchaser desires, are 
made out. Unless these are quite broad many dealers 
or manufacturers may not be able to comply with 
them and for this reason often submit specifications 
of their own, and thus the final specifications which 
form the basis of contracts must be somewhat modi¬ 
fied. 

In general, specifications may be divided into two 
parts: one part which deals with machinery and 
materials, and another which deals with the installa¬ 
tion work and results to be obtained. If certain 
materials are specified, and at the same time require¬ 
ments as to certain results are made, there is always 
a chance for disputes as to who is responsible in case 
the installation does not fulfill requirements. Unless 
the work is to be carried on under the supervision of 
a consulting engineer, it is best to give the contractor 
free choice of materials and hold him entirely re¬ 
sponsible for the final result. 


ELECTRICAL TABLES AND DATA 


217 


All specifications should be based upon the stand¬ 
ards of the engineering societies governing the par¬ 
ticular kind of work. The A. I. E. E. have standard¬ 
ization rules which govern everything electrical, but 
these do not largely concern themselves with safety 
rules. In this regard the National Electrical Code 
should be adopted as the standard and all material 
and workmanship should be specified to conform with 
its requirements. This is a reliable guide in every 
respect except that of economy and efficiency and 
suitability of systems, etc. It deals only with safety 
and reliability. 

It is best always to have some sort of a plan show¬ 
ing location of cut-out centers, switches, lights and 
motors, or any other parts about which there may 
afterwards be disputes. If there are no plans the 
location of cut-outs and other conspicuous elements 
should be mentioned in the specifications. They 
should also mention how much conduit, open or mold¬ 
ing work is to be used. Every item mentioned should 
form a clause and these should be numbered for 
reference. 

Where accurate calculations are to be made, all 
circuits and runs of wire should be measured and the 
specifications thoroughly read and considered. The 
estimator should take plenty of time to understand 
every phase of his job. As a reminder of the many 
items so easily overlooked, he should have prepared 
an estimate sheet on the order of that following which 
is furnished by courtesy of the National Electrical 
Contractors’ Association. Large apartments, hotels, 
etc., usually have many floors and rooms which are 
exact duplicates, and very careful measurements of 
one floor or room will answer for the whole building 
or that part of it which is typical. 

Table LXXIII shows approximate quantities of 
material used for rough wiring in average flats. 


In using this table, count all switches except those located in cutout boxes or on fixtures ns outlets. 

Ceilings are assumed to be 10 feet high; switches 4 feet from floor and brackets 6 feet. All runs have been figured at 
right angles, so that a small saving can be made with diagonal runs. 


218 


ELECTRICAL TABLES AND DATA 


tttfltda 

P P P P 
O O O o 

pr pr p-r 

CD CD CD CD 
r+ <r*- <r+- 
•0 CO CO GO 


o o o o 
TO 

i 


g p p § 

£-S3 S3 Q- 

p* ** 

to 


<?<???<? 


HH 
c b 
cr cr 

P P 

HIT* 

P o 
T3 O 

GO *0 


-- CD „ 

2.0 3 P 

S' ss S S 

‘EL'B.'B.os 
S' B » a 

on £,§•' 

JF?jf 

E-a 5 13 

o 


(W 


s-8* 

CD - 

* f 


!?<?<?£? 
p p p o 


55 55 55 55 ' 

Ercra-p- 

oT «T El 


o o o o 

CO 

Si 


o 

tr 


g P P g 
B-B B S- 
ClO-O-B 

3 ^H c *‘ 
CW C B 
b-ct- 

B B 
p o 

■o o 

C/3 “ 


K 

W 


B 

K 


O H 

3 B 


H 


O 
>=9 

O 
d 
M O 

* a 


> 

< 


> 

a 

H 

t- 

Ik¬ 

'S 


g 

► 

►5 

n 

5 

► 


00 

X 

o 


z 

c 

Ik¬ 

'S 

*s 

s> 

o 

g 

25 

H 


COCO 

O* o* 4 * • 

to to CO 
4 * 4 -** O 

to to CO 
00 00 to 


Ft. Single Wire. 

• • • to 
. . . to 


’JX 

• • • 

CD 

Ft. Twin Wire. 

• toco* 

• MH • 

• toco 

• KH 

• to CO 


Ft. Loom. 

t—* • • • 

• • 

M • • 

to; ; 

►—»• • 
CO; ; 


Ft. Moulding. 

co ♦—* • 

• CD *<I 

• -vJOO 


No. Insulators. 

to >-» to • 

GO tO • 

‘ H - 4 

to to 4 * 

k—k »—* 

to 4 ^ CD 


No. Tubes. 


tsO 


Cn 


Ft. Conduit-, 


No. Elbows. 


No. Outlet 
Boxes. 


No. Lock Nuts 

and Bushings. 


No. Couplings, 

Extra. 


O0HODf-*«f-* 


<*♦-0BHOOf- 


Lb. Nails. 


Oz. Brads. 


Rolls Tape, 

Each Kind. 




























































ELECTRICAL TABLES AND DATA 


219 


National Electrical Contractors’ Association Universal 

Estimate Sheet. 


Bid Goes to 
Address 


No. Lights. 

No. Switches. 

No. Circuits. 

No. Base Plugs... 
No. Telephones... 

No. Motors. 

H. P. Motors. 

No. Fixtures. 

K. W. Generator. 
Switchboard . ... . 


.Architect or Engineer. 

•Address Arch, or Engr. 

’.Name of Job or Building. 

•Location of Job of Building.. 

!See Mr.Telephone No. ... 

•Bid Must Be In by.M.. 

' Salesman .j. 


Estimate No... 
Sheet No. 

Date. 19.. 


Job No 


Material Estimated by Labor Estimated by Priced by Approved by 


Conduit, Rigid 
Conduit Elbows 
Conduit Bushings 
Conduit Straps 
Conduit Hangers 
Lock Nuts 
Conduit Flexible 
Conduit Fittings 
Conduit, Non-Metallic 
Ceiling Boxes 
Bracket Boxes 
Switch Boxes 
Floor Boxes 
Box Covers 
Fixture Hangers 
Cutout Cabinets 
Panelboards 
Metering Panels 
Meter Loops 
Cutout Boxes 
Asbestos 
Cut Out Blocks 
Fuse Plugs 
Enclosed Fuses 
Flush Switches 
D. P. Flush Switches 

3 Way Flush Switch 

4 Way Flush Switch 
Snap Switches 

D. P. Snap Switches 

3 Way Snap Switch 

4 Way Snap Switch 


Knife Switches 
Door Switches 
Pendant Switches 
Rubber Covered Wire 
Lead Covered Wire 
Fixture Wire 
• Special Wire 
Lamp Cord 
Reinforced Cord 
Packing House Cord 
Show Window Cord 
Molding Wood 
Molding Metal 
Molding Fitting 
Fixtures 
Clusters 
Key Sockets 
Keyless Sockets 
Wall Sockets 
Rosettes 
Socket Bushings 
Cord Adjusters 
Shades 
Shadeholders 
Adapters 

Attachment Plugs 

Lamps, Incandescent 

Lamp Guards 

Arc Lamp 

Cleats 

Knobs 

Tubes 


Screws 

Nails 

Toggle Bolts 

Annunciators 

Annunciator Wire 

Annunciator Cable 

Elevator Cable 

Bells 

Buzzers 

Push Buttons 

Silk Cord 

Door Openers 

Burglar Alarm 

Batteries 

Bell Ringers 

Telephones 

Telephone Cable 

Speaking Tube 

Whistles 

Letter Boxes 

Tape 

Solder 

Compound 

Acid 

Oil 

Car Fare 

Cartage 

Bond 

Drafting 

Inspection 

Incidentals 


Bid Sent to Following: 


Total 

Material 

Labor 

Overhead Expenses Per cent 
Profit Per cent 

Bid 




















220 ELECTRICAL TABLES AND DATA 

Figures 23, 24 and 25 will assist in illustrating the 
most economical manner of running wires for branch 
circuits. In Figure 23 the heavy black lines denote 
the mains, and at their terminals the cut-outs are 
located. It is never economical to push mains any 
farther than is necessary to enable one branch circuit 
to reach the far end of the space to be covered. In 
the arrangement shown in Figure 23 the greatest 
possible economy would be effected if a cut-out were 



Figure 23.—Comparison of Materials. 


provided for each circuit, but for various reasons 
this is not advisable. The next best arrangement is 
to provide a number of cut-out centers as shown in 
the figure, locating each cut-out in the center of the 
group it is to supply. 

In case a given number of lights are to be fed with 
wires running at right angles, the most economical 
arrangement can be found by running a straight line 
through the space covered at such point as to leave 
an equal number of lights on each side of it, as in 
Figure 24. 

If the lights are to be fed by diagonal runs, the 
shortest runs can be quickly found by bearing in 

















































ELECTRICAL TABLES AND DATA 


221 







mind that from the cut-out center, or from any outlet, 
this point in connection with any two other outlets 
forms a triangle and it is merely necessary to avoid 
using the longest side of this triangle. The position 





G 


B- 
Q 


43 


76 Ft 

—G 



Figure 24. 



of lamps shown in Figures 24 and 25 is identical, but 
Figure 25 requires about 10 per cent less material 
than Figure 24. The relative economy of running 
mains or branch circuits can be determined by Table 
LXXIV, which gives the equivalent in mains of vari* 
ous sizes and branch circuits of 660 watt capacity. 











222 


ELECTRICAL TABLES AND DATA 


TABLE LXXIY 

Showing Mains and Their Equivalent in No. 14 Branch 

Circuits. 


2 Wire 

Mains Branches 

2 ft. No. 14= 4 ft. No. 14 
2 ft. No. 12= 6 ft. No. 14 
2 ft. No. 10= 8 ft. No. 14 
2 ft. No. 8=10 ft. No. 14 
2 ft. No. 6=16 ft. No. 14 
2 ft. No. 5=18 ft. No. 14 
2 ft. No. 4=22 ft. No. 14 
2 ft. No. 3=26 ft. No. 14 
2 ft. No. 2=30 ft. No. 14 
2 ft. No. 1=32 ft. No. 14 
2 ft. No. 0=40 ft. No. 14 
2 ft. No. 00=50 ft. No. 14 
2 ft. No. 000=58 ft. No. 14 
2 ft. No. 0000=74 ft. No. 14 


3 Wire 

Mains Branches 

3 ft. No. 14= 10 ft. No. 14 

3 ft. No. 12= 12 ft. No. 14 

3 ft. No. 10= 16 ft. No. 14 

3 ft. No. 8= 22 ft. No. 14 

3 ft. No. 6= 32 ft. No. 14 

3 ft. No. 5= 36 ft. No. 14 

3 ft. No. 4= 44 ft. No. 14 

3 ft. No. 3= 52 ft. No. 14 

3 ft. No. 2= 60 ft. No. 14 

3 ft. No. 1= 64 ft. No. 14 

3 ft. No. 0= 80 ft. No. 14 

3 ft. No. 00=100 ft. No. 14 
3 ft. No. 000=116 ft. No. 14 
3 ft. No. 0000=148 ft. No. 14 


Street Lighting. —In villages and suburbs, the 
street lighting is often of a perfunctory nature. It 
consists often merely of an incandescent or arc lamp 
placed at each street intersection. Such lights should 
be over center of streets. In parks, the object of the 
illumination must be not merely the road or path, but 
fields and lagoons as well. At band-stands and sim¬ 
ilar places, arc lamps are preferable, but where the 
lights must be brought down under trees they are not 
very serviceable. Along curved driveways place 
lights on the outer curve; this will enable drivers to 
see farther, but will require more material. 

In business streets a very brilliant illumination is 
often desired. Tungsten lamps, installed on posts, 





ELECTRICAL TABLES AND DATA 


223 


are the most common illuminants at present where 
a permanent installation is contemplated. For tem¬ 
porary effects festoons are much used. The systems 
upon which such lights are operated will usually be 
governed by that which is already in use. The fol¬ 
lowing points should be noted in connection with 
street lighting: Large units are most economical in 
first cost, but waste much of their light outside of the 
street. At street intersections this waste is not so 
great. Large units should always be hung high. A 
bright illumination, except on business streets, is not 
necessary, but the light should be white. For series 
incandescent lighting special lamps are always used. 
The thicker the filament the less will the flickering 
effect of low* frequencies affect them. For overhead 
work wires smaller than No. 6 are seldom used. No 
incandescent lamp should ever be used outside without 
a reflector to prevent light being wasted on the upper 
air. Time switches are often serviceable on street 
lighting. Those who undertake to install a system 
of street lighting should prepare themselves for an 
unlimited amount of annoyance from residents who 
imagine their trees will be ruined or who quarrel 
about the location of poles and lamps. 

Switches.—The standard height of switches in 
offices and residences is 4 ft. 6 in. above finished floor. 
If switches of the push button type are used the white 
button should be uppermost. Switches should con¬ 
tain sufficient metal to prevent a temperature rise 
of over 28° C. (50° F.). There should be a contact 
surface of about 1 sq. in. for every 75 amperes. To 
obtain this contact surface large capacity switches 
are made up of a number of blades in parallel. This 
arrangement also allows better radiation. The fol¬ 
lowing table shows the capacity of single blades of 
dimensions given, the clip being assumed as of som j 
width. 


224 


ELECTRICAL TABLES AND DATA 


TABLE LXXY 

Width, in.. 4 f * I f 1 1 U U 1| H if 
Amperes ....8 15 30 58 85 115 150 180 215 280 330 395 

These widths will not determine capacity of switch 
unless the temperature rise is within the limits. 
Below are given the dimensions and spacings of knife 
switches as required by the N. E. C. Over all dimen¬ 
sions of standard knife switches as made by the George 
Cutter Company are given on pages 226 and 230. 

Spacings and Dimensions .—Spacings and dimen¬ 
sions must be at least as great as those given in the 
following tables: 


TABLE LXXYI 


Not over 125 volts d. c. and a. c. 

For switchboards and panel boards: 





Minimum 




separation of 
nearest metal 

• 


Width and Thickness 


parts of 

Minimum 


Clips 


opposite 

break 


Blades and Hinges 

polarity 

distance 

30 amp..., 

-in. ix B 3 j in. 

1 in. 

| in. 

60 amp..., 



1£ in. 

1 in. 


TABLE LXXYII 



Not over 125 volts d. c. and 
For individual switches: 

a. c. 




Inch 

Inch 

Inch 

Inch 

30 

amp. 

1 X B 3 ? 

4 

1 

60 & 100 

amp. 


n 

u 

200 

amp. 


2i 

2 

400 & 600 

amp. 


2| 

2 i 

800 & 1000 

amp. 


3 

2i 

A 300- 

-ampere switch with 

the 

spacings 

of the 


200-ampere switch above may be used on switchboards. 









ELECTRICAL TABLES AND DATA 




TABLE LXXVIII 


250 volts only d. c. and a. c. 
For all switches: 


30 amp. 

Inch 

Inch 

Inch 

Inch 

1-J rJL 

l x s^J 

If 

U 

TABLE 

Not over 250 volts d. c. 

LXXIX 

nor over 500 

volts 

a. c. 

For all switches: 

Inch 

Inch 

Inch 

Inch 

30 amp. 

. . fxl 

fxfs 

2* 

2 

60 & 100 amp. 



2i 

2 

200 amp. 



21 

21 

400 & 600 amp. 



2f 

21 

800 & 1000 amp. 



3 

2f 


A 300-ampere switch with the spaeings of the 200- 
ampere switch above may be used on switchboards. 

Cut-out terminals on switches for over 250 volts 
must be designed and spaced for 600-volt fuses. 

TABLE LXXX 

Not over 600 volts d. c. and a. c. 

For all switches: 

Inch Inch Inch Inch 


30 amp.fx$ fx^g 4 3$ 

60 amp. 4 31 

100 amp. 41 4 


Auxiliary contacts of either a readily renewable 
or a quick-break type or the equivalent are recom¬ 
mended for d. c. switches, designed for over 250 volts, 
and must be provided on d. c. switches designed for 
use in breaking currents greater than 100 amperes 
at a voltage of over 250. 

For 3-wire direct current and 3-wire single phase 
systems the separation and break distances for plain 
3-pole knife switches must not be less than those 
required in the above table for switches designed for 
the voltage between neutral and outside wires. 











CUTTER KNIFE SWITCHES 


226 


ELECTRICAL TABLES AND DATA 


to 

CM 

0) 

f-t 

g) 

• rH 

A 

© 

CQ 


on 

<x> 




O 


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£ 

m 

o 

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CT 


fm 


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o 

<H 



• rH 



£ 
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A 


d 

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X ° 

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cS o 
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P w 


0 d' 


x) 

i 3 

> -w 

03 


H 


P^ 


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£0 j 

®P h 

CD U 

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!GP 0 • 

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u 


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©H 

IO 

> .d 

°Q, 

o 


ci 


u 

o 


<m y 

>n°! 
2 •<! 
«c w U 




R^d 

£§H 

»o 

M 



*H<* 

HH 

>JN .JM 








Hto 

Ho 

B 


H-t 

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COpD 

cnto 

P*0 

• 

• 

» 

9 

fW 

■HH< 

►JM kJM 








HO 

HO 

* ico 

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i-W 

•-W 

eoto 

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«to 

Hri 

H* 

h* 

H2 

H(M 

into 

into 

t** 


Hoo 

hh 

HN 

«*r 







rH 

rH 

rH 

rH 

rH 

H|aO 

HH< 




M)M 

t>to 

oto 

HIM 

Hoo 

•W 

CO 

CO 


T}H 


r}H 

Tft 

IO 

IO 

to 

to 

C5|00 

ml* 


H» 

ento 

W H 

h|» 

"H 

H|00 

h|» 


rH 

rH 

CM 

CM 

CO 


IO 


IO 

io 

CO 


into 

t^loo 

HH 

H|M 


H|M 

enW 

hH< 

HM 

HHI 




to 

to 


L- 

t- 

CO 

OO 

OO 


10* 


C5W 


enhn 

HH 

enW 


1H^ 


CM 

CM 

co 

CO 



IO 


IO 

IO 

to 


into 




into 






ento 

H|H 

«to 

H|M 

onto 

H*h 

hH< 

H|M 


• 

9 

rH 

rH 

CM 

CO 

Tfl 


to 

to 

t- 

• 

• 

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h* 

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hW 


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to 

to 

t— 

t- 

oo 

OO 

oo 

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HM 

h|m 

nW 

• 

mm 


enhH 

HW 

• 

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CO 

CO 

CO 

• 


io 

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to 

• 

9 

t-w 

H» 


H|M 

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eoH< 


HW 

HHt 

Hhf 

CM 

CM 

co 

CO 

CO 


Ttn 

IO 

IO 

to 

t- 

eoH 1 

h* 


HH 

h|m 

H|M 

esH* 


HW 

HHI 

HHI 

rH 

CM 

CM 

CO 

co 


TH 

IO 

IO 

to 



H|M 

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nH 

rf# 

hHi 

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«to 

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t- 

CO 

C5 

CM 

CO 


IO 

to 

t- 

00 

00 




rH 

rH 

rH 

rH 

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rH 

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to 

t>. 

o 

o 

CM 

co 

CM 

CO 

T* 

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rH 

rH 

rH 

rH 

rH 

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rH 

rH 

o 

o 

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o 

o 

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o 

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to 

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* 




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CM 












f30-ampere switches for use on 500 volts A. C. will take dimensions of 60-ampere 
ches, except for fuse spacings. 

*300-ampere switches, unfused. 


ELECTRICAL TABLES AND DATA 227 


to 

o 

1—1 

M 

O 

00 

05 

4x 

* 

to 

to 


—4 

>•0 

o 

o 

o 

o 

o 

o 

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• 

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00 

00 


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CD 

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00 

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p ' 




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■ o 

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2 ® 

• 

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to 

1-1 

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l-i 




d2 

o 

h*< 

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o 

00 


iM 

• 

l-i 

CD 

05 

OS 




h m 

CT 


Ocp 

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cop 

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4P 










cp 














O tc 

• 

• 

CD 

oo 

oo 

05 

• 

Ol 

44 

to 

l-i 

50 V. 
D.C. 
r A.C. 

• 

• 

|4P 

H— 

CP 

ocp 

itp 

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4P 

ocp ocp 

MM 












o 

• 

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12 

4-1 

l-i 

11 

CD 

• 

00 

05 

iP 

4» 

600 V. 
D.C. 
r A.C 

• 

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4P 

a* 

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i4P 

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• 

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to 

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1-1 

t—i 



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t-i 


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CD 

• 

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• 

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CP 

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• 

ocp 

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to 

to 

to 

to 


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l-i 

1-1 

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GOO V. 

D.C. 
or A.C. 

• 

• 

00 

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iM 

t—i 

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lP 

1-1 

o 

• 

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i4p 

hH 

CP 

Mp 

ocp 

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djc* 

Cl 


CO 

to 

to 

to 

to 

M 

h-i 

1-1 

l-i 



►d 

OCp 

Otp 

ocp 

CCp 

i(4-i 

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ocp 



4P 

oop 


CO 

to 

to 

to 

to 4-1 • 

4-i I-* u Jr) 


i(-p 

MP 

4P 

4p • 

4P 4P CCp ^ 


05 

to 

to 

tO 4-i 

t-l 

4-i 4-i _ d 

MM 

MM 

4P 

4P 

MM 

*4- 4p Ocp mM 


TABLE LXXXI—Continued 



















228 


ELECTRICAL TABLES AND DATA 



Figure 26. —Cutter Knife Switches Paragon Type. 








































































































































































Figure 27.—Cutter Knife Switches Type FF. 


ELECTRICAL TABLES AND DATA 


229 



91 

S\'v • 

4 

<5 

7k 





TO 










A 





& r 


K 

1 <5 



























































































































































230 


m 

w 

o 



o 


CJ 

® 

P 

to 

E 

© 

© 

m 


ELECTRICAL TABLES AND DATA 


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r-^f 


eow 

Hto 

c0)00 



kM 

h co 

CO rJH rfrl 

HH 


TH 

10 

LO 

CD 

to CO CS 






_to 



into 

jp 


V*£> 










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nht 

r^rH 

Hh 

Hto 

HH 

C5(X) 


H» 

rto 


Hh 




rH 

CJ 

CO 

co 

rH 

LO 

lO 

LO 

to 

to 

to 

00 

OO 










rH 









f 

k; .u 
o^-< 

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Ha> 

rW 

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rj-jt 

e^H 1 

toH< 

HH< 

HH 

HH 

HH> 

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rH 

LO 

to 

to 

t- 

t- 

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OO 

OO 

CO 

CS 

cs 




ofl u 














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© o 

















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US 


















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into 







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cs 

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into 

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to 

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t <{l < 

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f30-ampere switches for use on 500 volts A. C. will take dimensions of 60-ampere 
switches, except for fuse spacings. 

*300-ampere switches, unfused. 


ELECTRICAL TABLES AND DATA 


'f* W M H M * 

OOOCr»OGOOi^OOtOI-i —Z a 

OOOOOOOOOOOC1CO 5« 
OOOOOOOOOOOOOtJ" 


to 

l! 

2 

h- 4 

MM 

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KM 

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M 

ocM 

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k|m 

# 

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oc|u 

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wu 

OM 

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or 

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CO 

to 

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MM 

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oc|oi 


CC|Gd 


11 

11 

co 

co 

c© 

OO 

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Ol 

4^ 





Mm 

HM 

iMm 

CtfLO 

oc|oi 

rf-iM 

a|M 


KM 

km 

M 

KM 





. . . . 4x 

CO 

tO 

o • 

00 

oi 

CO 

to 

• • • • iHM 

w® 

Mr 

fr 

OHm • 

iHm 

ohoi 

m!m 

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Mm 

I—* 

M 

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KM 

KM 




• • • • 

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at 

CO • 

O 

00 

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OHM • 


oHct 

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to 

h - 4 

• 

• 

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hH 

OCjM 

iHw • 

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acp 

Mm 





apt 








h- 4 

KM 

h" 4 





4^ 

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V- 4 

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Mm 


CHW 







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CO 

CO 

to • 

h- 4 

KM 

KM 


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odH 

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K|C0 


to 

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KM 

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to 

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ct' 3 

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to 

to 

to 

KM 

KM 

h- 4 



• • • • £0 

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CO 

• 

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M 


ohm • 

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cr 







to 

to 

to 

to 


KM 

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• 

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LO 

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• 

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%r 

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Sh 

oo|cn 

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CO 

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to 

to 

to 

KM 

KM 


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M-* 

M-* 


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K*- 4 

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1(4-* 



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m M 


tn M 

2 . U 

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231 


TABLE LXXXII—Continued 











232 


ELECTRICAL TABLES AND DATA 


Switchboards. —The best material for mounting 
switches and bus-bars is marble. Slate may be used, 
but metal veins may cause trouble. A liberal allow¬ 
ance of space should be allowed back of board, and 
its panels should be kept well above the floor. Where 
more than one machine is connected it is customary 
to operate them in parallel on d. c. For dimensions 
of bus-bars, switches and fuses, see those headings. 
It is customary to provide the following instruments, 
etc., for good switchboards: One main three pole 
switch for each generator, where there are several 
operated in parallel. One ammeter for each gen¬ 
erator, or an ammeter arranged for connection to 
each machine. A voltmeter which may be connected 
to any machine, and also be used as a ground detector. 
One field rheostat for each machine. Sufficient pilot 
lights to illuminate board properly. In some cases 
also a wattmeter measuring the total current. 

Alternating current boards are also often equipped 
for parallel running, but not always. In some cases 
the board is divided and fitted with throw over 
switches so that either generator may supply every¬ 
thing connected, or only a part of it, as desired. 

The following equipment is commonly used: Main 
switch for each generator. Synchronizing lamps, or 
synchroscope. Frequency indicator. Power factor 
indicator. Voltmeter to be used as with d. c. machines. 
An ammeter for each phase, and also for each gen¬ 
erator. Exciter equipment. Wattmeters. To these 
must of course be added the necessary fuses and 
switches. The N. E. C., however, does not require 
fuses on a. c. generator or their exciters. If prac¬ 
ticable, light and power circuits should be kept 
separate. 

Symbols. —The following are the symbols recom¬ 
mended by the American Institute of Electrical 
Engineers. 


ELECTRICAL TABLES AND DATA 


233 


The following notation is recommended: 


Name of quantity 


Symbol 


Unit 


Voltage, e.m.f., potential difference.... 

Current . 

Resistance . 

Reactance . 

Impedance . 

Admittance . 

Conductance . 

Susceptance . 

Power .*.. 

Capacity. 

Inductance . 

Magnetic flux. 

Magnetic density. 

Magnetic force. 

Length . 

Mass . 

Time . 


E, e, 

I, i, 

R, r, 

X, x, 
Z, z, 

Y, y, 

G , g, 

B, b, 

p > P, 

C, c, 

L, 


B 

H 


L, 1, 

M, m, 
T, t, 


volt 
ampere 
ohm 
ohm 
ohm 
mho 
mho 
mho 
watt 
farad 
henry 
maxwell 
gauss 
gilbert per cm. 
cm. or inch 
gm. or lb. 
second or hour 


Em, Im and Bm should he used for maximum cyclic 
values, e, i and p for instantaneous values, E and I 
for r. m. s. values, and P for the average value or 
effective power. These distinctions are not necessary 
in dealing with continuous current circuits. Vector 
quantities are preferably represented by bold face 
capitals. 

Testing. —It is assumed that the reader of this 
work is familiar with the general principles employed 
in testing, and therefore no attempt will be made to 
explain methods of using the various instruments. 
The list given in the following pages is intended as a 
reminder of the various instruments available for 
different purposes. Those about to undertake testing 
work with which they are not entirely familiar are 
advised to consult this list, and select those instru¬ 
ments needed. Consult Standardization Rules of 
A. I. E. E. and N. E. C. and make tests in conformity 
with their standards. 



















234 


ELECTRICAL TABLES AND DATA 


STANDARD SYMBOLS FOR WIRING PLANS 


As adopted and recommended by t he National Electrical Contractor* 
Association of the United States. 




<na 

8-01 




Ceiling Outlet; e'ectric only. Numeral in center indicate* 
number of standard 16 c. p. incandescent lamps. 

Ceiling Outlet r combination. 4-2 indicates 4-16 c. p. stand¬ 
ard incandescent lamps and 2 gas burners. 

Bracket Outlet; electric only. Numeral in center indicates 
number of standard 16 c. p. incandescent lamps. 

Bracket Outlet; combination. 4-2 indicates 4-16 c. p. stand¬ 
ard incandescent lamps and 2 gas burners. 1 

Wall or Baseboard Receptacle Outlet. Numeral in center 
indicates number of standard 16 c. p. incandescent lamps. 

Floor Outlet. . Numeral in center indicates number of stand* 
ard 16 c. p. incandescent lamps. 

Outlet for Outdoor Standard or Pedestal; electric only. 
Numeral indicates number of stand. 16 c. p. incan. lamps. 

Outlet for Outdoor Standard or Pedestal; combination, 
6-6 indicates 6-16 c. p. stand, incan. lamps; 6 gas burners. 

Drop Cord Outlet. 



One Light Outlet, for lamp receptacle. 


<3 


Arc Lamp Outlet, 

Special Outlet, for lighting heating and power current, as 
described in specifications. 


cOo^ 


Fan Outlet. 


S. P. Switch Outlet. 


D. P. Switch Outlet. 


3 3-Way Switch Outlet. 

O 4 4-Way Switch Outlet. 


Show as many symbols as there are 
switches. Or in case of a very 
large group of switches, indicate 
number of switches by a Roman 
numeral, thus: Si XII; meaning 
12 single pole switches. 

Describe type of switch in specifi¬ 
cations, that is. 

Flush or surface push button or 
snap. 


Copyright 1906 by the National Electrical Contractors* Association of ta<9 
United States. Published by permission. 








ELECTRICAL TABLES AND DATA 


235 


STANDARD SYMBOLS FOR WIRING PLANS 

4fl adopted and recommended by the National Electrical Contractors 
Association of the United States. 

Automatic Door Switch Outlet. 


S' 

^ Electrolier Switch Outlet. 


Meter Outlet. 


[Distribution Panel. 



Junction or Pull Box. 


f Motor Outlet; numeral in center indicates horsepower* * 


[Motor Control Outlet. 



Transformer. 


► Main or feeder run concealed under floor. 


' Main or feeder run concealed under floor above. 


Main or feeder run exposed. 


■ ■ ■ 1 Branch circuit run concealed under floor. 

Branch circuit run concealed under floor above. 
—“ *“* Branch circuit run exposed. 

♦ — •Pole line. 


• Riser. 

Suggestions in Connection with Standard Symbols for Wiring Plans. 

Indicate on plan, or describe in specifications, the height of all outlets 
located on side walls. 

It is important that amplespafle be allowed for the installation of mains, 
feeders, branches and distribution panels. 

It i.3 desirable that a key to the symbols used accompany all plana. 

If mains, feeders, branches and distribution panels are shown on tha 
plans, it is desirable that they be designated by letters or numbers. 
















236 


ELECTRICAL TABLES AND DATA 


STANDARD SYMBOLS FOR WIRING PLANS 

As adopted and recommended by the National Electrical Contractors 
Association of the United States. 

Telephone Outlet; private service. 

Telephone Outlet; public service. 

Bell Outlet 

Q Buzzer Outlet. 


H 

8 




—© 
HD 
ffl 


a 


Push Button Outlet; numeral indicates number of pushes* 
Annunciator; numeral indicates number of points* 

Speaking Tube. 

Watchman Clock Outlet. 

Watchman Station Outlet. 

Master Time Clock Outlet. 

Secondary Time Clock Outlet 
Door Opener. 

Special Outlet; for signal systems, as described in specifications 


11 | 11 (Battery 


Outlet. 


Circuit for clock, telephone, bell or other service, 
run unde'• floor, concealed. 

Kind of service wanted ascertained by symbol to 
which line connects. 


( Circuit for clock, telephone, bell or other service, 
run under floor above concealed. 

Kind of service wanted ascertained by symbol to 
which line connects. 

NOTE—If other than standard 16 c. p. incandescent lamps are desired, 
specifications should describe capacity of lamp to be used. 




ELECTRICAL TABLES AND DATA 


237 


TABLE LXXXIII 
Terminals.—George Cutter Co. 
Square Type, Cast. 

(See Figure 28.) 



Figure 28.— Terminals. 


Standard Dimensions. Inches 


Amps. 

Wire Size 

A 

B 

30 

8 

2 

I 

50 

5 

1 

f 

75 

3 

I 

f 

100 

1 

II 

f 

150 

00 

II 

b 

175 

000 

1 

II 

200 

0000 

It's 

1 

250 

300000 

lg 3 2 

1 

300 

350000 

If 

U 

350 

400000 

u 

If 

400 

500000 

If 

If 

500 

750000 

If 

If 

600 

1000000 

2 

If 

700 

1250000 

21 

2 

800 

1500000 

21 

2 

1000 

2000000 

2f 

21 


C D E F G 

b fs f ^ & 

I I 1 3*2 I 3 S 

T 3 5 I If 3 9 2 3 9 2 

TS II 1J II 3 9 2 

f If Tl8 II 

I II H b II 

I it if II II 

A II if II II 

t 1 2 I II 

I 7 s llV 21 A If 

I II 2§ II f§ 

A If 2f 1A ££ 

A 1A 3 1A ff 

I If 31 1* II 

I 2 31 II II 

i 2i 3* ii n 








































238 

Amps 

30 

50 

75 

100 

150 

175 

200 

250 

300 

350 

400 

500 

600 

700 

800 

1000 

30 

50 

100 

150 

200 

300 

400 

600 

25- 50 

75-100 

150 

200 

300 


ELECTRICAL TABLES AND DATA 


Round Type, Cast. 


Wire Size 

A 

B 

c 

D 

E 

F 

a 

8 


9 

16 

f 

A 

f 

A 

A 

5 

ff 

f 

i% 

§ 

If 

3 7 2 

A 

3 

if 

. 7 

3 

TS 

f 

If 

3 9 2 

A 

1 

It's 

1 

32 

f 

If 

ff 

3 9 2 

00 


1 

f 

5 

8 

If 

A 

fl 

000 


If 

f 

11 

16 

If 

f 

ff 

0000 

n 

If 

f 

f! 

If 

fi 

fl 

300000 

i* 

If 

1 f 

ff 

If 

ff 

fl 

350000 

if 

If 

re 

1 

2 

3 

¥ 

fl 

400000 

if 

If 

i 5 e 

If 

2f 

ff 

fl 

500000 

if 

If 

if 

If 

2f 

ff 

13. 

32 

750000 

2J 

Iff 

f 

If 

3 

1* 

ff 

1000000 

2f 

2f 

f 

If 

3f 

1A 

ff 

1250000 

2f 

2f 

3 

¥ 

If 

3| 

1* 

ff 

1500000 

2f 

2f 

f 

2 

3f 

If 

ff 

2000000 

2f 

2f 

f 

2f 

4 

If 

if 


Right Angle Type, 

Cast. 




8 

f 

f 

f 

A 

A 

A 

A 

5 

f 

f 

f 

f 

f 

3*2 

re 

1 

it 

f 

A 

f 

1 

ff 

3 9 2 

00 

1 

f 

A 

f 

If 

A 

ff 

0000 

If 

1 

f 

ff 

If 

ff 

fl 

350000 

If 

If 

f 

1 

If 

f 

fl 

500000 

If 

If 

f 

If 

If 

ff 

fl 

1000000 

2 

If 

IS 

If 

2 

1A 

ff 


Wrought Type. 





6 

A 

A 

A 

A 

f 

A 

A 

3 

f 

A 

f 

f 

If 

f 

i 

0 

if 

ff 

f 

f 

If 

f 

ff 

000 


7 

3 

f 

f 

If 

f 

§ 

300000 

If 

If 

f 

f 

2 

f 

fl 


« 



ELECTRICAL TABLES AND DATA 


239 


Ammeter. —In choosing an ammeter one must con¬ 
sider whether it is for a.c., d.c. milli-amperes, full 
current, or shunt. . Special instruments are made for 
each of these conditions; they are also made record¬ 
ing. 

Bond Tester. —This is an instrument made espe¬ 
cially for testing the conductivity of rail bonds and 
rails. 

Cable Testing Set. —Usually an instrument capable 
of locating faults in cables without cutting into the 
cable. 

Capacity Testing Sets. —A portable insulating and 
capacity testing set is made by the Leeds and North- 
rup Co. Other cable testing sets can also be used for 
this purpose. 

Current Transformers. —These instruments are 
used with a. c. circuits where large currents are to be 
measured; also with wattmeters. 

Dynamometer. —This is a special form of galva¬ 
nometer which may be used for very accurate measure¬ 
ments of either voltage, current or watts. It can also 
be used for testing capacity and inductance and other 
tests for which volt or ammeters may be used. It is 
used mostly for a.c. work. 

Electrolytic Conductivity Apparatus. —The inter¬ 
nal resistance of batteries can be measured by means 
of the Wheatstone Bridge, but slight errors are pos¬ 
sible. To avoid these errors special apparatus has 
been constructed. 

Electrometer. —This is an instrument the operation 
of which is based on electric charges; used in lab¬ 
oratories for measuring difference of potentials. 

Frequency Meter. —Such instruments are used to 
determine the frequency of a.c. circuits. They may 
also be used as speed indicators. 


240 


ELECTRICAL TABLES AND DATA 


Fault Finder. —This is a name given to certain 
special forms of testing instruments containing a bat¬ 
tery and resistances and arranged to facilitate testing. 

Galvanometer. —The galvanometer is a very deli¬ 
cate testing instrument and exists in a variety of 
forms. It is more delicate than the telephone re¬ 
ceiver for d. c., and where there is much noise, but 
for fluctuating currents the latter is more serviceable. 

Gauges. —Wire gauges are used for measuring the 
diameters of wires, sheet metal, etc. See description 
under this heading. 

Ground Detectors. —Voltmeters and lamps are used 
for this purpose, as well as special electrostatic in¬ 
struments. 

Hydrometer. —This instrument is frequently re¬ 
quired in testing battery solutions. 

Illuminometer. —Illuminometers are of various 
kinds. Some of them are very simple and somewhat 
crude; others are good photometers, a little more sim¬ 
ple and portable than the latter; usually calibrated 
in foot candles. 

Induction Standards. —Self and mutual induction 
standards are used in connection with the Wheatstone 
Bridge for comparing inductances. 

Iron Loss Watt and Voltmeters. —This is a special 
instrument made by the Westingliouse Co. for meas¬ 
uring the iron losses in transformers. 

Keys. —For high potential or precision work spe¬ 
cially constructed keys or switches are employed. 

Lamp and Scale. —For reflecting galvanometers a 
special lamp and scale are often required. 

Megger. —This is a trade name for a special testing 
set gotten out for general purposes. 

Meter Testing Sets. —These are special plugs and 
connections to facilitate the testing of wattmeters. 


ELECTRICAL TABLES AND DATA 


241 


Micrometer. —This instrument answers the same 
purpose as the wire gauge, but is much more accurate 
and can be used for very accurate measurements. 

Multipliers. —These are resistances intended to be 
placed in series with voltmeters and which enable the 
voltmeters to be used for the measurement of higher 
voltages. 

Ohm-meters. —This is a simplified form of Wheat¬ 
stone Bridge and is used for the same purposes; 
measuring resistances, detecting faults, etc. 

Oscillograph. —This is an instrument used for re¬ 
cording accurately the variation in the wave form of 
an alternating current or e. m. f. 

Permeability Meter. —The permeability meter is 
used for testing samples of iron as to their magnetic 
reluctance, or permeability. 

Phase Rotation Indicator. —This is an instrument 
used in determining direction of rotating field, or in 
connecting motors, etc. 

Photometer. —This device is used to measure inten¬ 
sity or degrees of illumination. Some photometers 
are cumbersome laboratory instruments; others are 
portable. 

Polarity Indicator. —This is an instrument used to 
determine the polarity of electric currents; also made 
to determine the polarity of magnets. 

Potential Transformer. —This is a piece of ap¬ 
paratus used mostly for reducing the voltage by a 
fixed ratio so as to bring it within the range of in¬ 
struments. 

Power Factor Meter. —This piece of apparatus indi¬ 
cates the phase relation between the current and 
e. m. f. of the circuit, or generator, to which it is 
connected. 

Pyrometer. —The pyrometer is used for measuring 
heat. Some pyrometers depend upon electrical prin- 


242 


ELECTRICAL TABLES AND DATA 


ciples for their action. They are sometimes used to 
determine the temperature of field coils. 

Resistances .—Separately mounted resistances are 
sometimes used in connection with the Wheatstone 
Bridge and other instruments to enlarge their scope. 

Rotating Standard .—This is a wattmeter in which 
a pointer moves rapidly, its movement being in pro¬ 
portion to the power consumed in the circuit at the 
time. It is especially designed to facilitate compari¬ 
son of meters with it. 

Sechometer .—This is an instrument used to measure 
coefficients of self-induction. 

Shunts .—These are used in connection with am¬ 
meters and so chosen that only a predetermined por¬ 
tion of the total current shall pass through the meter. 

Slide Wire Bridge .—This is a modification of the 
Wheatstone Bridge. 

Standardizing Set .—This is usually an arrange¬ 
ment of instruments of high grade which may be used 
to calibrate or standardize other instruments. 

Synchroscope .—This device indicates the phase dif¬ 
ference between two currents or e. m. f. *s to which it 
is connected. 

Tachometer .—This is a speed indicator, usually ar¬ 
ranged to be held against end of shaft. When fitted 
also with a stop watch, it is known as a tachoscope. 

Telefault .—This is a special type of testing instru¬ 
ment manufactured by Matthews & Bro., which en¬ 
ables certain tests to be made without cutting into the 
wires; can also be used for locating underground 
pipes. 

Telephone Receiver .—The receiver is very sensitive 
to fluctuations in current strength and is much used 
for testing. With d. c. it gives only one click when 
current is switched on or off. Where there is much 
noise it is somewhat handicapped. 



ELECTRICAL TABLES AND DATA 


243 


Thermometers .—These are used in testing ma¬ 
chinery and wires. Specially constructed instru¬ 
ments are mostly used. 

Voltameter .—An instrument measuring current 
strength by the amount of electrolyte decomposed. 

Volt-ammeter .—An instrument capable of measur¬ 
ing both current and voltage. 

Voltmeters .—They are used for measuring p. d. 
Not all are suitable for a. c. and d. c.; some are elec¬ 
trostatic, some read in milli-volts and are recording. 

Wattmeters .—These are used for measuring power. 
Not all of them are suitable for d. c. and a. c. 

Wheatstone Bridge .—This is the best known of all 
electrical testing instruments. With it more tests 
can be made than with any other device. It is, how¬ 
ever, cumbersome and more difficult to handle than 
many of the other instruments. 

Thawing Water Pipes.—Special stepdown trans¬ 
formers are generally used for a. c. and must have at 
least 200 amperes capacity for the smaller pipes and 
should have much more for larger ones. Storage 
batteries have also been used. 

Theatres.—A full treatise on this subject is given 
in “Motion Picture Operation, Stage Electrics and 
Illusions. ’ ’ 

Arc Pockets .—These should be wired with no 
smaller than No. 6; switched at the board, and open 
at the bottom to prevent accumulation of dirt. Large 
theatres can well use pocket capacity for twenty arc 
lamps. The pockets should be arranged off stage, as 
close to the scenery as practicable. Each pocket 
usually contains four circuits. 

Auditorium .—Some auditoriums are thickly stud¬ 
ded with lamps, the purpose being to produce dec¬ 
orative effects. In such cases frosted lamps are 
advisable. The actual illumination may be brought 


244 


ELECTRICAL TABLES AND DATA 


about by arc lamps, or large chandeliers. Unless dec¬ 
orative effects are striven for, one 50-watt lamp will 
furnish enough illumination for twenty seats. From 
two to ten fan motors should be provided for, accord¬ 
ing to size of theatre. It is impossible to arrange a 
system of direct lighting in connection with which 
some of the lights will not be in the range of vision 
of part of the audience at least. If the expense is 
not prohibitive cove, or indirect lighting, would be 
very serviceable. Cove lighting is very useful to show 
off decorations about proscenium arch. 

Balcony .—In the balcony or gallery, provision for 
several arc lamps should be made. These should also 
be controllable from the main board. The ceilings in 
balconies are usually low, and lights must be kept 
well back to avoid range of vision of spectators. Use 
inverted lighting or small c.p. lamps kept well up 
at ceiling. Provide for fan motors. 

Blinding Lights .—This is a row of lights sometimes 
placed about proscenium arch, the purpose being to 
blind the audience for a few moments to permit a 
quick change of scenery. Lamps of high intrinsic 
brilliancy should be used. If decorations are of a 
light color, or emergency lights must be kept burning, 
the plan is not very successful. Never frost lamps 
used for this purpose. 

Borders .—From one to six borders, according to 
size and pretensions of house, are installed. Feed 
borders to center. Leave cables long enough so bor¬ 
ders may be lowered to within five feet of stage floor. 
Use slow-burning wire and arrange for color circuits. 
Borders should be suspended by wire rope and in¬ 
sulated. Lamps are placed from six to twelve inch 
centers. The proportion of white and colored lamps 
is: two white, one red and one blue. Some borders 
are provided with a special circuit providing just 
light enough for rehearsals. 


ELECTRICAL TABLE'S AND DATA 245 

Bridges .—This is a name given to small galleries 
usually located at each side of proscenium and open¬ 
ing on stage side. Arc lamps are often operated 
from these bridges and are pockets should be pro¬ 
vided. This is also a good place from which to con¬ 
nect stage chandeliers. 

Bunch Lights .—These lights are mostly fed out of 
stage pockets. The bunch circuits should be switched 
at the board, and some of them at least should be 
grouped with color circuits. Plugs used for incan¬ 
descent circuits on stago should not be interchange¬ 
able with arc lamp plugs. 

Canopies .—Most theatres are equipped with cano¬ 
pies in front of house. These are often studded with 
lights. Arrange for low-wattage lamps and have 
them frosted. Arrange lamps to be out of weather. 
Sometimes provision is made for lamps in glass signs; 
1320 watts will be allowed per circuit with these 
lights if they are properly wired for. 

Chandeliers .—Large chandeliers are often used in 
theatres. These should be hung so they may either 
be raised or lowered for renewal of lamps. 

Curtain .—In .large cities all theatres are fitted with 
heavy asbestos and steel curtains. These usually re¬ 
quire motors to operate them. In some cities hy¬ 
draulic operation is required. In some cases the drop 
curtain is also operated by motor. 

Damper .—All good theatres are provided with 
stage dampers wdiich can be instantly opened in case 
of a fire on the stage. It is customary to hold the 
damper closed by an electromagnet, and to place a 
switch on each side of stage, said switch when opened 
releasing the magnet and allowing the damper to 
open. 

Dressing Booms .—Arrange dressing room illumina¬ 
tion without cords if possible. Provide circuit for 
^Atirou. Cover each lamp with a strong locked 


246 


ELECTRICAL TABLES AND DATA 


guard. Arrange lights so that each side of face is 
illuminated by at least one lamp. Door switches are 
useful in dressing rooms. 

Emergency Lighting .—Every theatre should have 
an emergency lighting system capable of furnishing 
sufficient light for the audience to leave the house in 
case the main system fails. The emergency system 
should be entirely independent of the other lighting 
and in no way connected with it. It is customary to 
provide capacity for about one 25-watt lamp for each 
400 square feet of auditorium space. To this emer¬ 
gency system may also be connected a sufficient num¬ 
ber of exit lights to indicate doors and fire escapes. 
Allow no key sockets, fan motors, or other devices on 
emergency lighting circuits. 

Fire Alarm .—Provisions for fire alarm should be 
made. It is customary to connect the stage with the 
box office through a signal circuit that can be used 
for various purposes. 

Fire Pump .—This is provided to insure good pres¬ 
sure in case of fire. It must be wired for in the most 
substantial and reliable manner. 

Fly Floor .—This is that part of the gallery above 
stage, from which stage hands operate the curtains. 
A few lights only are needed, but they should be 
located convenient for men lounging between acts. 

Footlights .—These form the most important and 
effective part of the permanently located stage lights. 
They must be very carefully located so as to illumi¬ 
nate the lower part of stage without obstructing the 
view of the audience. Lights are generally studded 
as thickly as possible, and about half of them arranged 
for white and the other half divided into two colors. 

Galleries .—On these pockets for arc lamps, etc., are 
usually provided. 

Grid .—This is the name given to that part of the 
rigging loft to which sheaves, etc., operating curtains 




ELECTRICAL TABLES AND DATA 


247 


and drops, are attached. Provide one light for each 
400 square feet. 

Lobby. —The lobby is usually very brilliantly illumi¬ 
nated, but the lights must be controlled by switches so 
that most of them may be turned out when the audi¬ 
ence is inside. Provide side outlets for picture illu¬ 
mination, etc.; also for portable signs. 

Orchestra Lights. —The largest theatres have about 
100 outlets for orchestra lights. Less than twenty 
should not be considered in any first-class house. 
Place fuses on switchboard and arrange control so 
that one of the musicians can control lights in dark 
scenes. 

Program Board. —This is an arrangement of lights 
by which the next number on the program can be 
given the audience. A special outlet at each side of 
stage should be provided for it. Run large conduit, 
as many wires must be accommodated. 

Proscenium Side Lights. —These lights are arranged 
at each side of proscenium opening on stage side. 
Sometimes they are wired for three colors. 

Retiring Rooms. —These are usually wired in imita¬ 
tion of homes, cozy comer effects, table lamps, etc. 
Illuminate pictures on walls. 

Stage Switchboard. —The stage switchboard is 
usually located on right hand side of stage, facing 
the audience, and it is preferable to elevate it above 
stage level. The wiring of a good board should be 
divided into four parts, each independent of the 
others. All of the house lights should be controlled 
by one main switch; the footlights and all of the 
upper part of stage lighting by another, and the 
stage pockets by a third. In addition to this there 
should be a division to which lights that remain in 
use all of the time are connected. The stage lighting 
is again divided into three color groups, the white 


248 


ELECTRICAL TABLES AND DATA 


lights being equal numerically to all of the colored 
lights. 

A list of the circuits which should be independent 
of all others and make up group four is given in the 
following: 

Dusting circuit. 

Ventilating motor circuit. 

Orchestra lights. 

Program lights. 

Fly floor lights. 

Pilot lights. 

Fig. 29 shows a well-laid-out switchboard. All 
of the lights in the auditorium are controlled by 
switches shown in the upper right hand corner, and 
all of these are under control of the main switch. 
House lights are usually operated as a unit. 

The stage pockets are controlled by the bank of 
switches shown at F. Lights burning off of stage 
pockets are generally controlled by special operators 
or by actors, so that switches need not be so very 
convenient to switchboard operator. He must, how¬ 
ever, have them under his control. In the arrange¬ 
ment shown in Figure 29 the white lights predom¬ 
inate in the ratio of two to one, and are laid out in 
two groups, A and B. Both groups are controlled by 
the switch C. The switches A and B do not control 
the lights at all if the smaller throw-over switches at 
the right are thrown downward. A diagram of these 
switches is given in Figure 30, where the switches 
B and C are indicated. The object of the switches 
A and B is to help in quickly increasing or decreasing 
the illumination on the stage. If in the beginning of 
a certain scene, for instance, only a small quantity of 
light is wanted, the low illumination may be obtained 
by throwing the proper switches dowti; the additional 


Fan motor circuit. 
Curtain motor. 
Dressing room circuits. 
Electric signs 
Rigging loft lights. 


ELECTRICAL TABLES AND DATA 


249 


illumination which will be wanted a few minutes 
later may be prepared for by setting the other switches 
needed to the upward position and at the proper 



Figure 29.—Stage Switchboard. 


moment closing switch B. In the same way, by a 
reversal of the process, the . illumination may be 
instantly reduced. This feature is very valuable in 
many stage settings. To throw off all of the white 

























250 


ELECTRICAL TABLES AND DATA 


lights the switch C must be opened. The switches D 
and E are main switches controlling the colored 
lamps. All lamps of one color should be connected to 
one or the other of these switches. 

From these three groups of switches circuits extend 
into all borders, proscenium side lights and footlights, 
so that the color scheme may be carried out in any 
or all of them. 

The handles of all switches in the same row should 
be of the same height. Switches should be extra 
heavy. Dimmer handles should be located directly 
above switches controlling them. 



The fuses or switches controlling lights not usually 
manipulated by switchboard operator are generally 
worked into the vacant spaces between the groups 
mentioned above. 

All branch circuits are preferably located behind 
the board. This will allow of trouble being instantly 
rectified. « 

Transformers.—The transformer capacity which 
must be provided ranges from .20 to .80 percent of 
the connected load. 

The full load efficiency of transformers varies from 
about 0.95 to 0.985. The smaller transformers are 


















ELECTRICAL TABLES AND DATA 


251 


less efficient than the larger, cost more per K. W., and 
give poorer regulation. Their installation is, however, 
much more economical in regard to wire. 

Transformers are properly rated in kilo-volt-am¬ 
peres (K.Y.A.). They cannot accurately be rated in 
K. W. (although this term is often used), because the 
wattage depends upon the power factor, which is 
governed mainly by the load and line to which the 
transformer is connected. The efficiency of a trans¬ 
former can be found by dividing the output by the 
input. 

The polarity is generally such that the current is 
entering the primary side at the same time it is leav¬ 
ing the secondary side corresponding to it. Oil 
cooled transformers are the most reliable, but should 
not be used where overflowing oil could do harm. 

The principal losses are the core or iron losses and 
the copper losses. The iron losses are the most impor¬ 
tant in transformers which are idle but connected 
the greater part of the time. Iron losses are continu¬ 
ous while the transformer is connected, whether it is 
delivering power or not. The copper losses take 
place only at time current is being used. The drop 
in voltage caused by them is proportional to the cur¬ 
rent, while the power loss is proportional to the 
square of the current. The iron losses are not of 
much importance at time of full load, but at this time 
the copper losses are the most disturbing. 

The core losses can be ascertained by measuring the 
current delivered to the primary side while the sec¬ 
ondaries are open and noting the percentage of this 
to the full load current. 

The copper loss can be found by applying voltage 
enough to the primary wires to cause the full load 
current to flow in the secondary, which must be short- 
circuited. This power must be measured by a watt 
meter and the percentage to the total power noted. 


252 


ELECTRICAL TABLES AND DATA 


Test all transformers for insulation before con¬ 
necting. 

All transformers should have their secondaries 
grounded, preferably at some neutral point. Shells 
of transformers should also be grounded. 

Tables for Determining the Most Economical Num¬ 
ber and Location of Transformers. —In a territory 
which has but few customers, and these somewhat 
scattered, each transformer constitutes a system by 
itself and is not connected to any other transformer. 
As the number of customers increases it becomes nec¬ 
essary either to extend the lines from one transformer 
or provide additional transformers and transfer part 
of the load to them. If the number of customers keeps 
on increasing, the mains from the various transformers 
soon meet, and may then be connected together, 
although, if transformers are far apart, there is no 
great advantage in this. Under these circumstances 
we have a number of transformers feeding a common 
line extending along a street. Finally, if the custom¬ 
ers still increase, or the load becomes greater, lines 
must be run on cross streets and these are connected 
to the others and we have a network of wires. In all 
three stages of the evolution of a secondary system of 
distribution, the determination of the most econom¬ 
ical arrangement of conductors and transformers is 
an important one. To keep the cost of wiring down 
to a minimum we must install a large number of small 
transformers. Small transformers are, however, more 
expensive in proportion to their capacity than large 
ones; and full load, as well as all-day efficiency, is also 
much lower. 

The most economical arrangement from the point 
of view of first cost of installment is that with which 
the investment for wires plus the investment for 
transformers is a minimum. There are three differ¬ 
ent conditions under which it may be necessary to 


ELECTRICAL TABLES AND DATA 


25S 


determine the most advantageous location of trans¬ 
formers : The first is that where a secondary system 
exists at the terminus of a primary extension. Since 
the secondary wires usually carry about ten times as 
much current as the primary, it is generally econom¬ 
ical to extend the primary line to the center of the 
secondary system. If, for instance, the secondary 
system consists of a straight run, by doing this we 
may use a wdre with four times the impedance that 
would be required if the transformer were at one end, 
or with a given wire, we may distribute four times the 
current for the same drop in voltage. 

These observations also hold good in case a number 
of transformers are to feed a continuous main. If 
we double the number of transformers, we quadruple 
the capacity of our wires or divide the drop by 4, 
provided, of course, they are evenly spaced through¬ 
out. 

When the secondary system finally reaches the net¬ 
work stage and, if we assume wires leading out from 
each transformer in four directions with an equal 
load in each, we should be able to do with wire of 
sixteen times the impedance of the first-considered 
case. There, is however, no great advantage in using 
such small wires, and at this stage large transformers 
are indicated. The whole network of wires is also 
interconnected so that current from any one trans¬ 
former tends to distribute toward any part in which 
an area of low potential develops. 

In order to facilitate calculations concerning sec¬ 
ondary lines the following tables have been prepared. 
By their use, if we assume even distribution of cur¬ 
rent, and even distance between distributing points, 
the drop at any part can be easily determined. In the 
lower table, LXXXVI, we have given the impedances 
for one ampere of 100 feet of line at 60 cycles and of 
various sizes of wire and at various separations. In 


254 


ELECTRICAL TABLES AND DATA 


the upper table, LXXXIY, are given multipliers with 
which to multiply these impedances. It is assumed 
that the secondary line extends over a certain number 
of poles, and that at each of these poles a certain num¬ 
ber of amperes are taken off. In order to use this table 
we select the horizontal line pertaining to the number 
of poles covered by the line, and in it select the num¬ 
ber found where the vertical line pertaining to the 
pole at which we wish to determine the drop, crosses 
it. Multiplying this number by the current assumed 
to be taken off at each pole and by the impedance 
of the wire, we obtain the drop in voltage at this 
pole. 

Example: We have a line extending over six poles 
(100 feet apart) and wish to find the drop at the third 
pole. We find the number 15 where the two lines 
cross; our wire is No. 1 and the separation 36 inches, 
while the current at each pole is 5 amperes; we have 
then for our drop 15x0.036x5= 2.7 volts. 

In case we wish to determine the smallest wire that 
can be used under similar circumstances or conditions, 
we use the formula 


in which Z is the impedance of the wire to be used, 
V the volts to be lost, I the current and K a number 
selected from the table as explained above. 

V 

Values of jjt have been calculated for all of the 

figures given in Table LXXXIV, and in order to find 
the smallest wire to deliver any amperage considered 
over any number of poles given, and at the desired 
loss, it is but necessary to follow the horizontal line 
pertaining to the proper constant K until it crosses 




ELECTRICAL TABLES AND DATA 


255 


the vertical line pertaining to the amperes to be trans¬ 
mitted, and at this place we find the impedance of 
the wire, which will give us the drop of 2.7 volts. By 
referring the impedance to the table of impedances 
we can then select the proper size of wire. These 
tables enable us to make trial calculations very rap¬ 
idly, and we can thus easily determine the most 
economical arrangement of conductors and trans¬ 
formers. 

Example: Suppose we have twelve poles spaced 
100 feet apart, and at each pole 5 amperes are to be 
used, while the drop must nowhere be greater than 
2.2 volts. Is it cheaper to feed this line with one large 
transformer or with two small ones? Placing the 
large transformer at about the center, we have six 
poles on one side and five on the other. In table 
LXXXIY for the sixth pole we find the constant 21, 
and in table LXXXV, where the line pertaining to 
this constant crosses with that pertaining to 5 amperes, 
we find the impedance 0.021. Looking up table 
LXXXVI for a corresponding impedance under 12- 
inch separation, we find 0.022 as the nearest, and that 
a 0000 wire is needed to come that near to our purpose. 
On the other side of the transformer we have only 
five poles, and the constant for this is 15, which in 
the same way we find requires an impedance of 0.029 
or a No. 0 wire. Making the calculations for two trans¬ 
formers, and for a continuous main, we may use the 
constant for the third pole, which is 6. Looking this 
up as before, we find an impedance of 0.07, which 
indicates a No. 5 wire continuous main for us. In 
order to find which is the cheapest we must now bal¬ 
ance 1,100 feet of No. 5 wire and two 30-ampere 
transformers against 600 feet of 0000 wire plus 500 
feet of No. 0, plus one 60-ampere transformer. 

Tables for calculating the most economical arrange¬ 
ment of transformers and conductors. 


256 


ELECTRICAL TABLES AND DAT 


TABLE LXXXIY 


Number of poles 
covered by line 
1 
2 

3 

4 
0 
6 


Transformer pole not counted. 
1st Foie 2nd 3rd 4th 5th 
1 


3 

4 

5 

6 


3 

5 

7 

9 

11 


6 

9 10 

12 14 15 

15 18 20 


6th 


21 


TABLE LXXXY 
V 

Showing Yalues of 


Con¬ 
stants Amperes 


K 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

12 

15 

1 

2.20 

1.10 

.733 

.550 

.440 

.367 

.314 

.275 

.244 

.220 

.183 

.147 

2 

1.10 

.550 

.366 

.275 

.220 

.183 

.157 

.138 

.122 

.110 

.091 

.073 

3 

.733 

.366 

.244 

.183 

.147 

.122 

.104 

.092 

.081 

.073 

.061 

.049 

4 

.550 

.275 

.183 

.137 

.110 

.092 

.078 

.069 

.061 

.055 

.046 

.037 

5 

.440 

.220 

.146 

.110 

.088 

.073 

.063 

.055 

.049 

.044 

.037 

.029 

6 

.366 

.183 

.122 

.092 

.073 

.061 

.052 

.046 

.041 

.037 

.030 

.024 

7 

.314 

.157 

.105 

.079 

.063 

.052 

.045 

.039 

.035 

.031 

.026 

.021 

9 

.244 

.122 

.081 

.061 

.049 

.041 

.035 

.031 

.027 

.024 

.020 

.016 

11 

.200 

.100 

.067 

.050 

.040 

.033 

.029 

.025 

.022 

.020 

.017 

.013 

12 

.183 

.092 

.061 

.046 

.037 

.031 

.026 

.023 

.020 

.018 

.015 

.012 

14 

.157 

.078 

.052 

.039 

.032 

.026 

.022 

.020 

.018 

.016 

.013 

.010 

15 

.147 

.074 

.049 

.037 

.029 

.024 

.021 

.018 

016 

.015 

.012 

.010 

18 

.123 

.061 

.041 

.031 

.025 

.021 

.018 

.016 

.014 

.012 

.010 

.009 

20 

.110 

.055 

.037 

.028 

.022 

.017 

.016 

.014 

.012 

.011 

.009 

.007 

21 

.105 

.052 

.035 

.027 

.021 

.017 

.015 

.013 

.012 

.010 

.009 

.007 


TABLE LXXXVI 

Showing Impedance Per Bun of 100 Feet; 60 Cycles. 


Separation in Inches. 

B. &S. i 6 12 24 36 

8 .126 .127 .128 .128 .128 

6 .081 .082 .083 .083 .084 

5 .066 .068 .069 .070 .071 

4 .051 .054 .055 .056 .057 

3 .041 .044 .046 .047 .048 

2 .032 .038 .040 .041 


Separation in Inches. 
B.&S. 4 6 12 24 36 

1 .026 .031 .033 .035 .036 

0 .021 .027 .029 .031 .033 

00 .017 .023 .026 .028 .030 

000 .014 .021 .024 .026 .028 

0000 .011 .019 .022 .025 .027 



ELECTRICAL TABLES AND DATA 


257 


An inspection of table LXXXVII will show that 
large transformers have a much higher all-day effi¬ 
ciency than small ones; for instance, by placing one 
4-K.W. transformer in place of four of 1 K.W.’s, we 
raise the efficiency (assuming the full load to be used 
three hours per day) from .84 to .91. In addition to 
this we also gain some in capacity, for the greater the 
number of customers connected to a transformer the 
greater will be the diversity factor. If we have a 
large number of small residences connected to one 
transformer, we need provide only about one-fourth 
the capacity of the connected load, whereas if we 
have one transformer for each customer we should be 
called upon for nearly the whole connected capacity. 
This gain in capacity comes in to such a marked 
extent only as long as we are dealing with trans¬ 
formers which are about fully loaded by one cus¬ 
tomer. As soon as the number of customers on any 
transformer reaches about twenty, they can be served 
with a transformer capacity which a larger number 
will not materially improve. A transformer capacity 
of one-fourth of the connected load will be sufficient 
for residence or flat lighting, but for stores, churches, 
and theatres a special study should be made as to 
what the maximum load of each is, and whether they 
are likely to occur at the same time. 

The use of larger transformers effects a saving in 
cost of transformers and in operating expenses, but 
entails a greater outlay for conductors, and to find 
which is the more economical we must balance the 
increased cost against the saving, and the most eco¬ 
nomical arrangement will be that in connection with 
which the value of the energy lost equals the interest 
on the investment of capital that must be made to 
save it. This must be found by trial calculations, and 
the various tables given will facilitate the calculations. 
It will, however, seldom be necessary to make such 


258 


ELECTRICAL TABLES AND DATA 


calculations, for in the first place the regulation of 
incandescent lamps limits us to a drop of about 2 
volts, which alone requires the use of comparatively 
large wires; in the second place very low efficiency 
comes in only where the transformers are idle a 
large part of the time. This condition, even with low 
efficiency, causes only a nominal loss of power. 

TABLE LXXXYII 

Table Showing All Day Efficiency of Various Commercial 
Sizes of Transformers Used for Various Hours Per Day. 


Equivalent Full Load Hours Per Day. 


K.W. 

1 

2 

3 

6 

9 

12 

18 

24 

1 

.66 

.78 

.84 

.89 

.92 

.93 

.94 

.96 

1* 

.70 

.81 

.86 

, .90 

.93 

.94 

.96 

.90 

2 

.72 

.84 

.88 

.93 

.94 

.95 

.96 

.96 

3 

.77 

.86 

.90 

.94 

.95 

.96 

.96 

.97 

4 

.79 

.87 

.91 

.94 

.95 

.96 

.96 

.97 

5 

.81 

.88 

.92 

.95 

.95 

.96 

.96 

.97 

7i 

.82 

.90 

.92 

.95 

.96 

.97 

.97 

.97 

10 

.83 

.90 

.93 

.96 

.96 

.97 

.97 

.97 

15 

.85 

.91 

.93 

.96 

.97 

.97 

.97 

.98 

20 

.86 

.91 

.94 

.96 

.97 

.97 

.97 

.98 

25 

.87 

.92 

.94 

.96 

.97 

.97 

.97 

.98 

30 

.87 

.93 

.95 

.96 

.97 

.97 

.97 

.98 

40 

.88 

.93 

.95 

.96 

.97 

.97 

.97 

.98 

50 

.89 

.94 

.96 

.97 

.98 

.98 

.98 

.98 


Trolley Lines.—Trolley wires range in size from 
0 to 0000; No. 0 is seldom used and 00 and 0000 are 
the most used. 

Standard voltages d-c. are 600 and 1,200; a-c., 3,300, 
6,600, and 11,000. A trolley system usually consists 
of feeders, trolley, and track return. The track return 
is often reinforced with negative feeders, and negative 
boosters are also used. (See also Electrolysis.) 

The height of trolleys ranges from about 15 to 22 
feet above the street; 22 feet is about the minimum 
allowed above tracks. 


ELECTRICAL TABLES AND DATA 


259 


Trolley sections range from a few hundred yards 
to several miles in length; heavy traffic zones are 
usually fitted with short sections. Poles range from 
30 to 40 feet in length, and wooden poles usually 
have 7-inch tops. The rake of poles varies from 
4 to 12 inches, according to nature of soil. 

There are various ways of trolley wire connections. 

The trolley may be run alone; it may be reinforced 
by feeders, trolley and feeders being in parallel, or 



Figure 31.—Train Sheet. 


it may be cut in sections, each section being fed by 
its own feeder. Alternating current systems do not 
usually have any secondary feeders. The drop allowed 
in d-c. systems ranges from 10 to 25 per cent; for a-c. 
systems it is 5 to 10 per cent. 

The current used at any point can be approximately 
determined by use of the “train sheet” illustrated in 
Figure 31. The height of the figure represents the 
length of the road or of any part of it to be considered. 
The width of it may represent the length of time 
during which the load is to be determined. 

For each car, or train, entering a section of trolley, 
draw a line beginning with the time the car enters 







































260 


ELECTRICAL TABLES AND DATA 


the section at the bottom and to meet the time point 
at the top at which it leaves that section. Draw lines 
beginning at the top of the figure in the same manner 
for all cars moving in the opposite direction. These 
lines will then cross, and to find the load on this 
section at any desired time, it is only necessary to 
draw an ordinate such as 1 at that point and count the 
number of car lines this crosses. This will give the 
number of cars fed over this section of trolley at that 
time, and the maximum current used can be easily 
determined. 

TABLE LXXXIX 

Table Showing Drop in Voltage Per 100 Amperes for Distance 

Given. 


Feet 


Miles 


B.&S. 

1,000 

2,000 

3,000 

4,000 

1 

2 

3 

4 

5 

0 

11.9 

23.8 

35.7 

47.6 

62.8 125.6 

188.4 

251 

314 

00 

9.44 

18.9 

28.3 

37.8 

49.8 

99.6 

149. 

199 

249 

000 

7.48 

15.0 

22.4 

29.9 

39.5 

79.0 

118. 

158 

198 

0000 

5.94 

11.9 

17.8 

23.8 

31.4 

62.8 

71.4 

126 

157 

C. M. 



D. C. Only. 





500000 

2.513 

5.0 

7.5 

10.5 

13.26 

26.5 

39.8 

53.0 

66.3 

1000000 

1.256 

2.51 

3.7 

5.0 

6.63 

13.3 

19.9 

26.6 

33.2 

2000000 

0.628 

1.26 

1.88 

2.51 

3.31 

6.6 

10.0 

13.2 

16.0 

3000000 

0.419 

0.84 

1.26 

1.67 

2.21 

4.4 

6.6 

8.8 

11.0 

4000000 

0.315 

0.63 

0.95 

1.26 

1.65 

3.3 

5.0 

6.6 

8.3 

5000000 

0.251 

0.50 

0.75 

1.00 

1.33 

2.65 

: 4.0 

5.3 

6.0 




TABLE LXXXX 





Table Showing P.D. on Return for 

Distances 

Above. 

Wt. of Rails 









Per Yard. 









2 Rails Used. 









40 

1.23 

2.46 

3.69 

4.92 

6.5 

13.0 

19.5 

26.0 

32.5 

45 

1.09 

2.18 

3.27 

4.36 

5.8 

11.6 

17.4 

23.2 

29.0 

50 

0.98 

1.96 

2.94 

3.92 

5.2 

10.4 

15.6 

20.8 

26.0 

60 

0.81 

1.62 

2.43 

3.24 

4.3 

8.6 

12.9 

17.2 

21.5 

70 

0.70 

1.40 

2.10 

2.80 

3.7 

7.4 

11.1 

14.8 

18.5 

80 

0.61 

1.22 

1.83 

2.44 

3.2 

6.4 

9.6 

12.8 

16.0 

90 

0.55 

1.10 

1.65 

2.20 

2.9 

5.8 

8.7 

11.6 

14.5 

100 

0.49 

0.98 

1.47 

1.96 

2.6 

5.2 

7.8 

10.4 

13.0 

110 

0.45 

0.90 

1.35 

1.80 

2.4 

4.8 

7.2 

9.6 

12.0 



ELECTRICAL TABLES AND DATA 


261 


The copper loss calculations are based on resistivity of hard 
drawn copper at 65° C 149° F. 

Rails are supposed to be standard and of specific resistance 
of 10 times that of copper. 

The losses in return circuit will be less than indicated 
because part of current returns through piping and earth. 
The combined drop in conductors and rails in parallel is 

_ 1 _ 

equal to — -f- -p- + where d, d 1 , d 2 , etc., represent the 

drop in the different conductors. 

The impedance of the rails at 25 cycles is said to be from 
6 to 7 times as high as the ohmic resistance. 

Impedance of trolley=1.5 times ohmic resistance. 


Tables LXXXIX and LXXXX have been especially 
prepared to facilitate calculations concerning drop in 
trolley circuits. Every trolley circuit consists of three 
elements: trolley proper, its feeders and the track 
return, and in order to effect distribution econom¬ 
ically, it is necessary to consider all of these sepa¬ 
rately. 

The upper part of table LXXXIX gives the drop 
in voltage caused by the trolley proper, and the lower 
part that caused by feeders, either overhead to rein¬ 
force trolley or underground to help out track rails, 
and table LXXXX the drop caused by the iron rails. 
The calculations have not been carried out for a-c. be¬ 
cause the circuits used for this method of transmission 
differ materially from d-c. systems. In a-c. systems 
the ground return may be considered as made up of 
a number of comparatively short sections, the current 
returning not to the central station but to its trans¬ 
former. This is also true of the trolley. With energy 
distributed at 25 cycles, the drop caused by the rails 
will be about 6.5 times as great as for d-c. and that 
in the trolley about 1.5 times. The drop caused by 




2G2 


ELECTRICAL TABLES AND DATA 


trolley and feeders, when they are in parallel, is 
equal to the reciprocal of the sum of the reciprocals 
of their lines. This is also the case with track rails 
and their reinforcement. 

As far as these are used in series the various losses 
must be added. 

The use of the tables can perhaps he best made 
clear by an example. 

Example: The train sheet shows that 1,200 am¬ 
peres will be required on a certain section of trolley 
one mile long and fed in the center by a feeder two 
miles long. The loss at far end of trolley must not 
exceed 15 per cent of the voltage, which is 600. The 
rails weigh 100 lbs. per yard, and the difference in 
potential between any two points must not exceed 
5 volts. What size of feeder and reinforcement of 
track rails will be necessary? 

Table LXXXIX shows that a 0000 trolley wire will 
cause a drop of 31.4 volts in one mile per 100 amperes. 
Our trolley is fed in the center and must be con¬ 
sidered one-half mile long; each half carries half of 
the current, viz., 600 amperes; therefore, the drop 
caused by a 0000 trolley will be six times the drop in 
half a mile, or, according to our table, 94.2 volts. 
This alone is more than 15 per cent of our voltage, 
600, hence we must divide our trolley into shorter 
sections. Making two sections out of the same length, 
or feeding it in two places, will give us a loss equal 
to 300 amperes for one-fourth mile, or just one- 
fourth of what we had before, viz., 23.6 volts lost in 
trolley. 

We have next to deal with the size of feeder, and 
are allowed a loss of slightly over 60 volts in it. The 
loss in feeders two miles long is given in table 
LXXXX, and we may use any feeder the loss of 
which, multiplied by 12, does not exceed 67 volts. 


ELECTRICAL TABLES AND DATA • 263 

12 times 6.6 equals 79.2, and is the loss caused by a 
2,000,000-cm. cable. This we must not use, but the 
next larger one will give us a loss of only 52.8, and 
this, added to the trolley loss, makes a total of 76.4 
volts. If it is desired to lose the full 90 volts a 
smaller trolley wire may now be considered. 

The loss in one mile of 100-lb. track is 2.6 volts 
per 100 amperes, which makes 31.2 for 1200; a 
5,000,000-cm. cable causes a drop of twelve times 
1.33, or 15.96 volts. The drop caused by both in 
parallel will be the reciprocal of the sum of the 
reciprocals. By the table of reciprocals we find the 
reciprocal of 31.2 is, roughly, 0.032051, and that of 
15.96 is 0.062500. Adding these, we have 0.094, ap¬ 
proximately. The number corresponding to this from 
the same table is 10.6, which is more than two times 
too high. Let us now consider the use of two 5,000,- 
000 cables. The drop in the cables will be just half 
of what it was before, or about 8. The reciprocal of 
8 is 0.01250; this added to 0.032 gives us 0.157, and 
the number corresponding to it is about 6.4. Tliis is 
still above what we require, but it must be borne in 
mind that not all of the current returns over the rails 
and negative feeders, hence, this will give us about 
the right p.d. The loss in trolley lines, track, and 
feeders can be lessened very much by increasing the 
number of substations from which they are fed, and 
the most economical arrangement can be determined 
by the same calculations laid out for locating trans¬ 
formers. 

Underground Construction. —Underground con¬ 
ductors are usually lead encased and as the lead is 
not very strong it is best to run the conductors in some 
form of conduit which protects them and facilitates 
removal in case of trouble. These conduits usually 
consist of some kind of clay, concrete or fiber, and 
their heat conductivity is generally not as good as 


264 ELECTRICAL TABLES AND DATA 

that of moist earth. Conduits arranged as shown in 
Figure 32 carry away more heat than those shown 
at Figure 33, but if there are many of them they also 
require more trench area. 

All conduits should be arranged to drain, and at 
suitable intervals should be provided with splicing 
chambers. If space between them is to be filled 
with concrete they must be anchored to prevent 
floating. 





o 


Q 


[O MQlO 


Figure 32. 


Figure 33. 


Underground Ducts. 


The following tables and information is taken from 
Handbook No. 17 of the Standard Underground 
Cable Co. (Copyright by Standard Underground 
Cable Co., 1906). 

Recommended Current Carrying Capacities for 
Cables, and Watts Lost per Foot, for each of four 
equally loaded single conductor paper insulated lead 
covered cables, installed in adjacent ducts in the 
usual type of conduit system where the initial tem¬ 
perature does not exceed 70° F. (21.1° C.), the 
maximum safe temperature for continuous operation 
being taken as 150° F. (65.5° C.). 



ELECTRICAL TABLES AND DATA 265 


TABLE LXXXXI 



Safe 

Cur¬ 

rent 

W T atts 

Dost 

Per 

Size 
B. & S. 

Safe 

Cur¬ 

rent 

Watts 

Lost 

Per 

Size 

Safe 

Cur¬ 

rent 

Watts 

Lost 

Per 

Size 

in 

Ft. at 

or 

in 

Ft. at 

Circular 

in 

Ft. at 

B. & S. 

Amp. 

150° F. 

C. M. 

Amp. 

150° F. 

Mils. 

Amp. 

150° F. 

14 

18 

0.97 

2 

125 

2.77 

900000 

650 

5.71 

13 

21 

1.03 

7 

146 

3.00 

1000000 

695 

5.86 

12 

24 

1.09 

0 

168 

3.23 

1100000 

740 

6.01 

11 

29 

1.15 

00 

195 

3.46 

1200000 

780 

6.13 

10 

33 

1.25 

000 

225 

3.69 

1300000 

820 

6.25 

9 

38 

1.39 

0000 

260 

3.92 

1400000 

857 

6.37 

8 

45 

1.53 

300000 

323 

4.22 

1500000 

895 

6.49 

7 

53 

1.67 

400000 

390 

4.61 

1600000 

933 

6.61 

6 

64 

1.85 

500000 

450 

4.91 

1700000 

970 

6.73 

5 

76 

2.08 

600000 

505 

5.16 

1800000 

1010 

6.85 

4 

91 

2.31 

700000 

558 

5.36 

1900000 

1045 

6.97 

3 

108 

2.54 

800000 

607 

5.56 

2000000 

1085 

7.09 


Assuming that unity (1.00) represents the carrying 
capacity of single-conductor cables, the capacity of 
multi-conductor cables would be given by the fol¬ 
lowing : 

2 Cond., flat or round form, 0.87; concentric form, 
0.79. 

3 Cond., triplex form, 0.75; concentric form, 0.60. 

The following experiment on duplex concentric 

cable of 525,000 c.m. indicates clearly the danger in 
subjecting tliis type of cable to heavy overloads of 
even short duration. The cable was first heated up 
by a current of 440 amperes for five hours. An over¬ 
load of 50 per cent was then applied, the results in 
degrees Fahrenheit above the surrounding air being 
as follows: 


• 

Time from start 

0 min. 15 min. 

Inner 

condr.. . 

70° 

84° 

Outer 

condr.. . 

55° 

65° 

Lead 

cover... 

31° 

35° 


30 min. 

45 min. 

60 min. 

90 min. 

98° 

111° 

123° 

142° 

76° 

85° 

94° 

108° 

40° 

45° 

49° 

57° 



266 


ELECTRICAL TABLES AND DATA 


As it is the final temperature reached which really 
affects the carrying capacity, the initial temperature 
of surrounding media must be taken into account. 
If, for instance, the conduit system parallels steam 
or hot water mains, the temperature of 150 F., which 
we have assumed in the table to be the maximum for 
safe continuous work on cables, will be reached with 
lower values of current than would otherwise be the 
case; and as 70 is the actual temperature we have 
assumed to exist in the surrounding medium prior to 
loading the cables, any increase over 70 must be 
compensated for by reducing the current. 

For rough calculations it will be safe to use the 
following multipliers to reduce the current carrying 
capacity given in table LXXXXI to the proper value 
for the corresponding initial temperatures. 

Initial temp. F. 70° 80° 90° 100° 110° 120° 130° 140° 150° 
Multipliers ...1.00 0.93 0.86 0.78 0.70 0.60 0.48 0.34 0.00 

When a number of loaded cables are operating in 
close proximity to one another, the heat from one 
radiates, or is carried by conduction, to each of the 
others, and all are raised in temperature beyond what 
■would have resulted had only a single cable been in 
operation. And if the cables occupy adjacent ducts 
in a conduit system of approximately square cross- 
section laid in the usual way, the centrally located 
cable or the one just above the center in large installa¬ 
tions (A in Figure 32) will reach the highest tem¬ 
perature. This is equivalent to saying that its cur¬ 
rent carrying capacity is reduced and while this re¬ 
duction does not amount to more than 12 per cent 
(as compared with the cable most favorably located, 
Z>, Figure 32) in the duct arrangement given it may 
easily assume much greater proportions where a large 
number of cables are massed together. 




ELECTRICAL TABLES AND DATA 


267 


Assuming that not more than twelve cables, ar¬ 
ranged as shown in Figure 32, can be used, the aver¬ 
age carrying capacity may be taken as the criterion 
for proper size of conductor, and for cables of a 
given type and size the carrying capacities of all 
cables, even though placed in adjacent ducts, will be 
represented by the following figures, taking unity as 
the average carrying capacity of four cables. (See 
Table LXXXXI.) 

Number of cables 2 4 6 8 10 12 

Multiplier .1.16 1.00 0.88 0.79 0.71 0.63 

Becommended Power Carrying Capacity in Kilo¬ 
watts of Delivered Energy .—The tables below are 
based on the carrying capacities of cables as given in 
Table LXXXXI. A power factor of unity was used 
in the calculations and hence the values found in the 
lower table are correct for direct current. For alter¬ 
nating current the kilowatts given must be multiplied 
by the power factor of the delivered load. 

Units. —Synopsis of units and symbols in general 
use. 

Defining Equation 


Unit 

Name 

Sym¬ 

bol 

Direct 

Current 

Alternating 

Current 

Electromotive 
force Volt 

E, e 

IR 

IZ 

Current 

Ampere 

I, i 

E-r- R 

E -7- Z 

Resistance 

Ohm 

R, r 

E-M 

V Z2 — X2 

Power 

Watt 

P 

El 

E I X p. f. 

Impedance 

Ohm 

Z, z 


V R 2 + X2 

Reactance 

Ohm 

X, x 


VZ2-R2 

Inductance 

Henry 

L, 1 

<1>-I 


Capacity 

Farad 

C, c 

Q-E 

Q-E 

Quantity 

Coulomb 

Q, q 

I X time 

I X time 

Admittance 

Mho 

Y, y 


I — Z = V G2 + B2 

Conductance 

Mho 

G, S 

I-rR 

R-t-Z2= VY2 — B 

Susceptance 

Mho 

B, b 


X — Z2 == V Y2 — G2 









26S 


ELECTRICAL TABLES AND DATA 


TABLE LXXXXn 

. Three Conductor, Three-Phase Cables. 
Size in ’ 


B. & S. Volts. 



1100 2200 3300 4000 6000 11000 13200 

22000 




Kilo-Watts. 




6 

92 

183 

275 

333 

549 

915 

1098 

1831 

5 

109 

217 

326 

395 

652 

1087 

1304 

2174 

4 

130 

260 

390 

473 

781 

1301 

1562 

2603 

3 

154 

309 

463 

562 

927 

1544 

1854 

3089 

2 

179 

358 

536 

650 1073 

1788 

2145 

3575 

1 

209 

418 

626 

759 1253 

2088 

2506 

4176 

0 

240 

481 

721 

874 1442 

2402 

2884 

4805 

00 

279 

558 

836 1014 1674 

2788 

3347 

5577 

000 

322 

644 

965 1172 1931 

3217 

3862 

6435 

0000 

372 

744 1115 1352 2231 

3717 

4462 

7435 

250000 

413 

827 1240 1503 2480 

4132 

4960 

8264 


Single Conductor 

Cables, 

A. C. 

or D. 

C. 





Volts. 






125 

250 

500 

1100 

2200 

3300 

6600 

11000 




Kilo-Watts. 




6 

8.0 

16.0 

32 

70 

141 

211 

422 

704 

5 

9.5 

19.0 

38 

84 

167 

251 

502 

830 

4 

11.4 

22.8 

45 

100 

200 

300 

601 

1001 

3 

13.5 

27.0 

54 

119 

238 

356 

713 

1188 

2 

15.6 

31.2 

62 

138 

275 

413 

825 

1375 

1 

18.3 

36.5 

73 

161 

321 

482 

964 

1606 

0 

21.0 

42.0 

84 

185 

370 

554 

1109 

1848 

00 

24.4 

48.8 

97 

215 

429 

644 

1287 

2145 

000 

28.1 

56.3 

113 

248 

495 

743 

1485 

2475 

0000 

32.5 

65.0 

130 

286 

572 

858 

1716 

2860 

300000 

40.4 

80.8 

162 

355 

711 

1066 

2132 

3553 

400000 

48.8 

97.5 

195 

429 

858 

1287 

2574 

4290 

500000 

56.3 

112.5 

225 

495 

990 

1485 

2970 

4950 

600000 

63.1 

126.3 

253 

556 

1111 

1667 

3333 

5555 

700000 

69.8 

139.5 

279 

614 

1228 

1841 

3683 

6138 

800000 

75.9 

151.8 

304 

668 

1335 

2003 

4006 

6677 

900000 

81.3 

162.5 

325 

715 

1430 

2145 

4290 

7150 

1000000 

86.9 

173.8 

348 

764 

1529 

2294 

4587 

7645 

1100000 

92.5 

185.0 

370 

814 

1628 

2442 

4884 

8140 

1200000 

97.5 

195.0 

390 

858 

1716 

2574 

5148 

8580 

1400000 

107.1 

214.3 

429 

943 

1885 

2828 

5656 

9427 

1500000 

111.9 

223.8 

448 

985 

1969 

2954 

5907 

9845 

1600000 

116.6 

233.3 

467 

1026 

2053 

3079 

6158 

10263 

1700000 

121.3 

242.5 

485 

1067 

2134 

3201 

6402 

10670 

1800000 

126.3 

252.5 

505 

1111 

2222 

3333 

6666 

11110 

2000000 

135.6 

271.3 

543 

1194 

2387 

3581 

7161 

11935 


ELECTRICAL TABLES AND DATA 


269 


Ventilation.—Ventilation for the purpose of pro¬ 
viding a certain quantity of fresh air to occupants of 
rooms or shops requires the apparatus to be in use 
continuously while the rooms are occupied, regardless 
of temperature. Where it is provided mainly to carry 
off surplus heat, it is used only in warm weather. The 
capacity in such cases must be sufficient to take care 
of the hottest weather. 

The quantity of air moved by any fan varies 
directly as the speed, but the power required to run 
the fan varies as the cube of the speed. The net 
result is that the cost of moving different volumes of 
air by any given fan varies about as the square of the 
speed at which the fan must operate to move it. This 
is the theoretical relation, but this is somewhat dis¬ 
turbed by the difference in efficiency of large and 
small motors operating at various speeds. Owing to 
the above facts it is often a difficult task to decide 
whether it is more profitable to install a small, cheap 
fan and run it at a high rate of speed, or to provide 
a more expensive one and operate it at a lower cost 
per unit of air moved. Which is the more profitable 
in the long run depends upon the number of hours 
per year the fan is to be used at its various speeds. 
In any case the most economical ventilator will be the 
one in connection with which the cost of energy saved 
per year will equal the interest charge upon the in¬ 
vestment of capital necessary to provide it in place of 
the cheapest fan which can do the work. The follow¬ 
ing tables are taken from publications of the American 
Blower Co. and give all the necessary data for com¬ 
parison of various fans. In order to find the most 
economical fan select the smallest fan capable of mov¬ 
ing the requisite amount of air and note the K. W. 
necessary to run it (divide H. P. given by 1.3). Next 
select some larger fan and note the K. W. necessary 
to move the same volume of air with this fan and sub- 


270 ELECTRICAL TABLES AND DATA 

tract it from the first. The next step is to find the 
value of the annual saving, by multiplying the number 
of hours per year this power is used by the rate per 
K. W. Having found this, if we divide it by the rate 
of interest applicable, we shall obtain the sum of 
money which we can afford to spend to substitute 
this fan in place of the smallest one we were consid¬ 
ering. The rate of interest by which we must divide 
is determined by the number of years the installation 
is to remain in use and is as follows: 

One year, 1.06 per cent; 2 years, .57; 3 years, .40; 
4 years, .32; 5 years, .27; 6 years, .24; 7 years, ,21£; 
8 years, .20; and 9 years, .18J. 

We have now the following formula by which we 
can determine the amount of capital which can with 
profit be invested in a larger fan: 

K. W. - k. w. xlixr 


where C = capital to be invested; K. W. -k.w. = the 
saving in energy per hour, and h and r = the number 
of hours per year and rate per K. W. hour of energy. 

In case the fan is used intermittently at various 
speeds the calculations should be made accordingly, 
since the power required at high speeds is much 
greater than at low speeds. The capacity of a fan 
used only to provide a sufficient quantity of fresh air 
is best determined by allowing from 30 to 50 cubic 
feet of air per minute for each adult, and from 20 
to 35 for each child. In special places such as hos¬ 
pitals this quantity is often doubled. The maximum 
quantities given will secure ample ventilation for all 
ordinary persons. In public places such as toilet 
rooms, waiting rooms, etc., it is customary to require 
from three to six changes of air per hour. 



f 

ELECTRICAL TABLES AND DATA 271 

TABLE LXXXXIII 

“Ventura” Disc Ventilating Fans. 

General Capacity Table.—American Blower Co. 

Capacities, Speeds and Horse Powers with Unobstructed 

Inlet and Discharge. 

No. of Velocity of Air in Feet per Minute, 

Fan 600 900 1200 1500 1800 2100 


Cu. Ft. Per Min.. 950 1420 1895 2370 2840 3320 

3 Pres. Ins. W. G.. .0225 .055 .09 .1406 .2025 .2755 

R. P. M. 625 980 1255 1565 1880 2190 

H. P.0097 .036 .079 .153 .265 .42 


C. F. M. 1620 2430 3240 4050 4860 5670 

4 Pres, ins.0225 .055 .09 .1406 .2025 .2755 

R. P. M. 470 735 945 1175 1410 1645 

H. P.0168 .062 .13 .262 .455 .72 


C. F. M. 2500 3750 5000 6250 7500 8750 

5 Press. Ins.0225 .055 .09 .1406 .2025 .2755 

R, P. M. 375 585 755 938 1125 1310 

H. P.026 .095 .207 .405 .701 1.10 


C. F. M. 3560 5350 7125 8900 10700 12500 

6 Press. Ins.0225 .055 .09 .1406 .2025 .2755 

R. P. M. 315 492 632 786 945 1100 

H. P.037 .136 .295 .575 1.00 1.59 


C. F. M. 4800 7200 9600 12000 14400 16800 

7 Press. Ins.0225 .055 .09 .1406 .2025 .2755 

R. p. M. 268 419 537 669 803 936 

H. P.05 .182 .398 .776 1.345 2.13 


C F. M. 6250 9375 12500 15600 18750 21850 

8 Press. Ins.0225 .055 .09 .1406 .2025 .2755 

R p. M. 234 366 470 584 702 817 

H. F.065 .237 .516 1.01 1.75 2.77 


C. F. M. 7875 11800 15700 19650 23600 27500 

9 Press. Ins.0225 .055 .09 .1406 .2025 .2/55 

r p. M. 209 326 419 521 626 730 

H. P.082 .30 .65 1.27 2.20 3.48 




































272 


ELECTRICAL TABLES AND DATA 


TABLE LXXXXIY 

Capacities, Speeds and Horse Powers with Resistance of 

Average Piping System. 

No. of Velocity of Air in Feet per Minute. 

Fan 600 900 1200 1500 1800 2100 


Cu. Ft. Per Min.. 950 1420 1895 2370 2840 3320 

3 Press. Ins. W. G.. .06 .15 .24 .37 .53 .73 

R. P. M. 716 1075 1435 1790 2150 2510 

H. P.022 .085 .18 .34 .59 .93 


C. F. M. 1620 2430 3240 4050 4860 5670 

4 Press. Ins.06 .15 .24 .37 .53 .73 

R. P. M. 540 808 1075 1345 1615 1885 

H. P.037 .14 .30 .58 1.00 1.59 


C. F. M. 2500 3750 5000 6250 7500 8750 

5 Press. Ins.06 .15 .24 .37 .53 .73 

R. P. M. 430 644 860 1075 1288 1500 

H. P.057 .21 .46 .90 1.54 2.45 


C. F. M. 3560 5350 7125 8900 10700 12500 

6 Press. Ins.06 .15 .24 .37 .53 .73 

R. P. M. 361 540 720 900 1080 1260 

H. P.082 .30 .65 1.27 2.20 3.50 


C. F. M. 4800 7200 9600 12000 14400 16800 

7 Press. Ins.06 .15 .24 .37 .53 .73 

R. P. M. 307 460 614 767 920 1075 

H. P.11 .40 .88 1.71 2.96 4.69 


C. F. M. 6250 9375 12500 15600 18750 21850 

8 Press. Ins.06 .15 .24 .37 .53 .73 

R. P. M. 268 402 535 670 803 940 

H. P.143 .53 . 1.14 2.23 3.85 6.10 


C. F. M. 7875 11800 15700 19650 23600 27500 

9 Press. Ins.06 .15 .24 .37 .53 .73 

R. P. M. 239 358 477 597 716 835 

II. P.18 .67 1.43 2.80 4.84 7.68 


Pressures noted are static pressures. 



































ELECTRICAL TABLES AND DATA 


273 


Where it is desired to reduce temperature or remove 
steam, etc., we must proceed to find the necessary 
capacity in another way. If we remove all of the 
heated air in a room and replace it with air from the 
outside Jrn the same length of time required to heat it, 
we shall reduce the temperature by one-half the dif¬ 
ference between that of the air in the room and the air 
brought in. From this fact we can deduce the fol¬ 
lowing method for determining the amount of air 
which must be taken out of a room in order to lower 
its temperature by any desired amount. Before the 
room has attained its full temperature place one or 
more thermometers at representative locations and 
note the temperature rise for any convenient length of 
time, but be sure that you are observing the maximum 
or general temperature rise which is to be ventilated 
for. By providing ventilator capacity to exhaust all 
of the air in the room one or more times in the same 
length of time in which the rise took place we shall 
reduce it according to the following tabulation which 
shows the number of degrees F. which the room tem¬ 
perature will be above the outside temperature with 
the number of changes taking place as given at the 
left in column 0. The column 0 is correct only when 
the room is so tightly closed that there is no natural 
ventilation. Under the other columns, headed by 
1, 2, 3, 4, and 5, are given the number of times the 
air must be changed to limit the temperature rise in 
room to the increases above the outside air as given 
in right hand section of table. Thus, if the increase 
in temperature allowed over the outside air is 30 
degrees and the air is naturally changing three times 
we must change it twelve times to limit the rise to 5 
degrees. 


274 


ELECTRICAL TABLES AND DATA 


TABLE LXXXXV 


Number of natural 

changes of air Increase in degrees F. 

assumed. above outside air. 


5 

4 

3 

2 

1 

0 

5 

10 

15 

20 

25 

30 

35 

40 

10 

8 

6 

4 

2 

1 

2i 

5 

n 

10 

12* 

15 

m 

20 

15 

12 

9 

6 

3 

2 

U 

24 

3f 

5 

6* 

n 

oo 

10 

20 

16 

12 

8 

4 

3 

£ 

If 

24 

3i 

H 

5 

5£ 


25 

20 

15 

10 

5 

4 

f 

u 

If 

2i 

3* 

3£- 

4f 

5 


Rule .—Determine difference in temperature be¬ 
tween outer and inner air which is to be ventilated for, 
and trace down column headed by this temperature 
until the allowable temperature of inner over outer 
air is reached. Next estimate number of natural 
changes taking place during the time of previous test 
and in section of table at left headed by this number 
trace down to same horizontal line in which the per¬ 
missible temperature was found. At this point the 
necessary number of changes in air will be found. 
These changes must take place in the same length of 
time in which the temperature rise took place. 

If there is a temperature rise accompanied by nat¬ 
ural ventilation the reductions in temperature given in 
Table LXXXXV, column 0, can be obtained only by 
doubling the number of changes taking place dur¬ 
ing the time that the rise in temperature was going 
on. 

Suppose, for instance, that a certain temperature 
rise takes place in an hour while during the same time 
the air is naturally changing ten times. The starting 
of the ventilator, if of sufficient capacity, immediately 



ELECTRICAL TABLES AND DATA 275 

ends all natural ventilation because every former out¬ 
let for air now becomes an inlet and all air passes 
through the fan. The number of changes which were 
naturally taking place now count for nothing and to 
reduce the temperature by one-half we must provide 
ten more changes per hour, i.e., change the air by 
means of the fan twenty times to obtain the effect of 
one change as given in column 0. Thus to find the 
number of changes necessary to obtain the effects given 
in the table in column 0 we must use the formula 
c= (axb) +a, where c = the number of changes that 
must be made; a = the number of natural changes tak¬ 
ing place, and b = the figure in column 0 which corre¬ 
sponds to the desired rise above the outside air at the 
difference in temperature. 

Example .—The increase in temperature in a certain 
room is 10 degrees above that of the outside air and is 
to be limited to 2^ degrees; the dimensions of the 
room are 100 x 20 x 12, while the natural change of air 
is assumed to be about three times per hour. What 
must be the capacity of the ventilating fan ? Tracing 
down in Table LXXXXV under 10 degrees to where 
2J is found, and then in the horizontal line to the left, 
to column pertaining to three changes of air per hour, 
we find the number 9, which signifies that we must 
have capacity to change the air nine times per hour, 
and since the room contains 24,000 cubic feet we must 
select a fan which can move 3,600 cubic feet per 
minute. 

Practical Hints .—Place ventilators at end of room 
opposite to where most of the air enters or so that all 
disagreeable air is nearest to the fan. Protect fan 
against wind blowing into it. Avoid noise by selecting 
large fans to operate at low speeds. Air in motion 
does not feel as warm as stationary air. It is best to 
provide a separate fan for kitchen ranges, etc., and 
attach it directly to hoods placed over such apparatus. 


276 


ELECTRICAL TABLES AND DATA 


In wide or square rooms provide several ventilators so 
as to secure a more uniform movement of air over the 
whole space. If fan capacity is small compared to 
size of room and cooling is the only consideration it is 
best to blow air into the room. An exhaust fan which 
does not change the air oftener than it is naturally 
changing has little effect. Even in well constructed 
places the air is supposed to change itself once per 
hour at least. 

Voltage Regulation.—In a network of wiring the 

regulation is always fairly good because a heavy de¬ 
mand at any point immediately causes current from 
all sides to rush in. The drop at feeder ends can be 
easily compensated for if they are all of the same 
length. If they are not of the same length they should 
be divided into groups of the same length and each 
group separately regulated. For d. c. work individual 
feeder regulators w r aste too much energy to be con¬ 
sidered except with very short lines. 

In long lines a booster is often installed. To deter¬ 
mine whether it is profitable to install a booster we 
must compare its cost and the losses due to its opera¬ 
tion, with the cost of increasing the size of conductors 
proportionately and the losses incident to the im¬ 
proved lines. Obviously this depends upon the length 
of the line, and the drop which may be allowed. De¬ 
termine investment for booster, interest and deprecia¬ 
tion and cost of operation and losses. This amount 
can be saved by the installation of proper feeders, 
and if we can obtain the larger feeders by an invest¬ 
ment of capital upon which the above sum will be the 
proper interest it will not be profitable to install the 
booster. 

For a. c. work individual feeder regulators are much 
used, and as they waste comparatively little energy, 
they may be used in each feeder and all feeders con¬ 
nected to a common line. Such regulators may be 


ELECTRICAL TABLES AND DATA 277 

arranged either to boost or choke. For low tension 
work, either a. c. or d. c., pressure wires are often run 
from the end of feeder back to switchboard to indicate 
the pressure at feeder end. The same object is also 
attainable by line drop compensators, or if the size and 
length of line be known the drop at the far end or 
any other point may be calculated from the number 
of amperes. 

The following table (LXXXXVI) is provided to 
assist in making the necessary calculations for the set¬ 
ting of a. c. line drop compensators, and also to deter¬ 
mine the drop in voltage occurring at any part of the 
line so that the voltage at the station may be raised 
correspondingly. 

To find the drop in voltage we may use the formula 
IZxd; in which I is the current in amperes; Z the 
impedance as given in the table for various sizes of 
wire and separation, and d the number of 1,000 feet 
of line. 

For line compensators it is necessary to find the 
percentage of the reactive, and ohmic drop. The same 
formula may be used substituting X or R for Z and 
dividing the result by the transmission voltage. This 
will give the percentage according to which the two 
sections of the compensator must be set. See detail 
instructions sent out with compensators. The values 
of Z, R and X are for 1,000 feet of wire. A single 
phase installation can be served by a single compen¬ 
sator, but then the drop will be double that given, or 
for 2,000 feet instead of 1,000 feet of wire. The same 
may be said of a two phase installation which is served 
by two compensators, but in two phase three wire, or 
in three phase systems, a compensator must be in¬ 
stalled in each wire, and a four wire three phase sys¬ 
tem requires four, so that in connection with these 
systems the value given in the table need not be 
doubled. 


278 


ELECTRICAL TABLES AND DATA 


TABLE LXXXXVI 


Table Showing Resistance, Reactance and Impedance of 1,000 
Feet of Wire of Sizes Given and at Various Separatipns. 


Separation of Wires in Inches. 

12 24 36 48 60 72 


B. & S. 

R 

X 

Z X 

Z 

X 

Z 

X 

Z 

X 

Z 

X 

Z 

8 

.627 

.126 

.640 .142 

.640 

.151 

.640 

.157 

.640 

.163 

.640 

.167 

.640 

6 

.397 

.120 

.415 .136 

.415 

.145 

.420 

.152 

.420 

.157 

.420 

.161 

.420 

5 

.314 

.118 

.345 .134 

.350 

.143 

.355 

.150 

.357 

.155 

.360 

.159 

.362 

4 

.250 

.115 

.275 .131 

.280 

.140 

.285 

.147 

.290 

.152 

.292 

.156 

.294 

3 

.198 

.112 

.230 .128 

.235 

.137 

.240 

.144 

.245 

.150 

.248 

.153 

.251 

2 

.157 

.110 

.190 .126 

.200 

.135 

.205 

.141 

.212 

.147 

.215 

.151 

.217 

1 

.126 

.107 

.165 .123 

.175 

.132 

.180 

.139 

.187 

.144 

.191 

.148 

.194 

0 

.100 

.104 

.145 .120 

.155 

.129 

.165 

.136 

.169 

.141 

.173 

.145 

.176 

00 

.079 

.102 

.130 .118 

.140 

.127 

.150 

.133 

.156 

.139 

.159 

.143 

.162 

000 

.063 

.099 

.120 .115 

.130 

.124 

.140 

.131 

.145 

.136 

.149 

.140 

.153 

0000 

.050 

.096 

.110 .112 

.125 

.122 

.135 

.128 

.138 

.133 

.140 

.137 

.146 


Weights of Materials in Pounds (Approximate ).— 
Aluminum, cu. ft., 167; cu. in., 0.095. For wires, see 
tables. 

Antimony, cu. ft., 418; cu. in., 0.242. 

Asphaltum, cu. ft., 84; gal., 11.2. 

Bismuth, cu. ft., 612; cu. in., 0.354. 

Brass, cu. ft., 522; cu. in., 0.302. 

Brick, cu. ft., 119; per thousand, 4500. 

Bronze, cu. ft., 537; cu. in., 0.311. 

Cement, loose, cu. ft., 88; bu., 95. 

Charcoal, cu. ft., 25; bu., 27. 

Coal, anthracite, piled loose, cu. ft., 52; bu., 56. 

bituminous, piled loose, cu. ft., 50; bu., 54. 
Coke, piled loose, cu. ft., 27; bu., 29. 


ELECTRICAL TABLES AND DATA 


279 


Concrete, cu. ft., 150; cu. yd., 4050. 

Copper, cu. ft., 555; cu. in., 0.321. For wires, see 
tables. 

Cork, cu. ft., 15.6. 

Crushed Stone, cu. yd., 2700. 

Earth, cu. ft., 109; cu. yd., 2943. 

Glass, cu. ft., 165. 

Gold, cu. ft., 1225; cu. in., 0.709. 

Gravel, cu. ft., 119; cu. yd., 3213. 

Ice, cu. ft., 56; cu. yd., 1512. 

Iridium, cu. ft., 1400; cu. in., 0.81. 

Iron, cu. ft., 490; cu. in., 0.225. For wires, see tables. 

Lead, cu. ft., 709; cu. in., 0.41. 

Limestone, cu. ft., 165; cu. yd., loose, 2700. 

Loam, cu. ft., 78; cu. yd., 2106. 

Mercury, cu. ft., 850; cu. in., 0.492. 

Nickel, cu. ft., 540; cu. in., 0.312. 

Oils, olive, gal., 7.6. 

“ cottonseed, gal., 8.0. 

“ linseed, gal., 7.8. 

“ turpentine, gal., 7.2. 

“ lard, gal., 7.9. 

“ whale, gal., 7.8. 

“ gasoline, gal., 5.7. 

“ petroleum, gal., 7.3. 

“ mineral lubricating, gal., 7.8. 

Paper, cu. ft., 56. 

Paraffine, cu. ft., 56; gal., 7.41. 

Pitch, cu. ft., 67; gal., 8.9. 




£80 ELECTRICAL TABLES AND DATA 


Platinum, cu. ft., 1340 

; cu. in., 0.718. 


Porcelain, cu. ft., 150; 

cu. in., 0.087. 


Salt, cu. ft., 60; gal., 8.04. 


Sand, 

CU. ft., 105; cu. 

yd., 2835. 


Silver, 

cu. ft., 653; cu. 

in., 0.377. 


Slate, 

cu. ft., 184; cu. 

in., 0.109. 


Sulphur, cu. ft., 125. 



Tantalum, cu. ft., 1040 

; cu. in., 0.60. 


Tar, cu. ft., 62.5; gal., 

8.33. 


Tin, cu. ft., 455; cu. in 

., 0.263. 


Tungsten, cu. ft., 1175; cu. in., 0.68. 


Water, plain, cu. ft., 62.5; gal., 8.33. 


< i 

sea, cu. ft., 79; 

gal., 10.3. 


Wood, 

ash, cu. ft., 46; per 1000 ft., 

3850. 

i i 

butternut, 

28; 

2330. 

< < 

cedar, “ 

38; 

3165. 

< < 

chestnut, 

39; 

3250. 

i < 

cypress, ‘ ‘ 

35; 

2915. 

-i < 

elm, ‘ ‘ 

36; 

3000. 

< < 

fir, 

35; 

2915. 

< < 

hemlock, ‘ ‘ 

27; 

2250. 

< < 

hickory, 

55; 

4600. 

< < 

lignum vitae, “ 

81; 

6750. 

< < 

mahogany ‘ ‘ 

36; 

3000. 

< < 

maple, “ 

50; 

4560. 

< < 

oak, ‘ ‘ 

47; 

3915. 

< t 

pine, white, “ 

25; 

2275. 

(( 

pine, yellow, “ 

45; 

3750. 

t ( 

poplar, ‘ ‘ 

24; 

2200. 

(t 

redwood, ‘ ‘ 

30; 

2740. 

«< 

spruce, 11 

28; 

2330. 

«< 

walnut, ‘ ‘ 

41; 

3400. 


Zinc, cn. ft., 420; cu. in., 0.243. 




ELECTRICAL TABLES AND DATA 


281 


Contents of Barrels or Bound Containers = average 
diameter squared x height x 0.7854. 

If measurements are taken in inches 

D 2 xHx 0.000454 = cu. ft. 

Z> 2 x H x 0.0034 =gal. 

D 2 x H x 0.000425 = bu. 

If cubic contents are known in feet, multiply by 
7.58 to obtain gallons, and by 0.936 to obtain bushels. 
To obtain cubic yards divide by 27. 

Welding.—From 30 to 60 H. P. per square inch 
area of weld to be made are used. This is the power 
required to be delivered to welder. The greater the 
capacity the shorter will be the time required to make 
a weld. In some cases only a few seconds are required. 

Wire Calculations.—This division contains the 
following tables: 

A table of carrying capacities of copper and alumi¬ 
num wires. 

A table showing carrying capacities of different 
combinations of wires. 

Table for determining the total wattage of groups 
of lamps or other devices usually rated in watts. 

Tables for calculating the amperage per H. P. of 
motors at various efficiencies and power factors. 

Tables showing maximum H. P. allowed on wires 
according to N. E. C. rules and carrying capacities. 

Tables for determining proper size of wire for a 
certain loss in voltage; copper and aluminum wires, 
direct current, and 60 and 25 cycles. 

Tables to facilitate determining the most economical 
conductors. 

Various tables showing physical properties of cop¬ 
per, aluminum, copper clad, german silver and steel 
wires. 

Tables showing outside diameters of wires and 
cables. 


282 


ELECTRICAL TABLES AND DATA 


TABLE LXXXXVIII 

Table of Allowable Carrying Capacity of Wires. 


B.&S. 

Rubber Insulation 

Other Insulations 

Circular 

Gauge 

Copper Aluminum 

Copper 

Aluminum 

Mils 

18 

3 

2 

5 

4 

1624 

16 

6 

5 

10 

8 

2583 

14 

15 

12 

20 

17 

4107 

12 

20 

17 

25 

21 

6530 

10 

25 

21 

30 

25 

10380 

8 

35 

29 

50 

42 

16510 

6 

50 

42 

70 

59 

26250 

5 

55 

46 

80 

67 

33100 

4 

70 

59 

90 

76 

41740 

3 

80 

67 

100 

84 

52630 

2 

90 

76 

125 

105 

66370 

1 

100 

84 

150 

126 

83690 

0 

125 

105 

200 

168 

105500 

00 

150 

126 

225 

189 

133100 

000 

175 

147 

275 

231 

167800 

0000 

225 

189 

325 

273 

211600 

Circular 

Mils 

200000 

200 

168 

300 

252 


300000 

275 

231 

400 

336 


400000 

325 

273 

500 

420 


500000 

400 

336 

600 

504 


600000 

450 

378 

680 

571 


700000 

'500 

420 

760 

639 


800000 

550 

462 

840 

705 


900000 

600 

504 

920 

773 


1000000 

650 

546 

1000 

840 


1100000 

690 

580 

1080 

901 


1200000 

730 

613 

1150 

966 


1300000 

770 

646 

1220 

1024 


1400000 

810 

680 

1290 

1083 


1500000 

850 

714 

1360 

1142 


1600000 

890 

748 

1430 

1201 


1700000 

930 

781 

1490 

1251 


1800000 

970 

815 

1550 

1301 


1900000 

1010 

848 

1610 

1352 


2000000 

1050 

882 

1670 

1402 



ELECTRICAL TABLES AND DATA 


283 


Carrying Capacities of Different Combinations of 
Wires .—Owing to the relatively different radiating 
surface of wires of different sizes the carrying capacity 
per circular mil is not the same for all wires, and 
where wires of different gauge number are to be con¬ 
nected in parallel this must be taken into account. In 
the following table this is done and the carrying ca¬ 
pacity of smaller wires at the current density allowed 
for the larger wires is given wherever the horizontal 
and vertical lines pertaining to any two wires cross. 
The number found at this place indicates the am¬ 
perage the smaller wire will have with the larger wire 
fully loaded. The figures are based on the carrying 
capacities given by the National Electrical Code. To 
find the proper wire to reinforce another which has 
been overloaded: Select the horizontal line pertain¬ 
ing to the larger wire and follow along this line until 
a number about equal to the necessary additional 
amperes is found. At the head of the vertical column 
in which this number is found will be found the gauge 
number of the proper wire to be used. 


284 


ELECTRICAL TABLES AND DATA 


TABLE LXXXXTX 

Table Showing Combined Carrying Capacity of Different 
Wires—Rubber Insulation 


Amps. B.&S. 

14 

12 

10 

8 

6 

5 

4 

3 

2 

1 

0 

00 

000 

0000 

15 

14 

15 














20 

12 

12 

20 













25 

10 

10 

15 

25 












35 

8 

8 

13 

22 

35 











' 50 

6 

7 

12 

20 

31 

50 










55 

5 

7 

11 

17 

27 

44 

55 









70 

4 

7 

11 

18 

28 

45 

55 

70 








80 

3 

6 

10 

16 

25 

39 

50 

64 

80 







90 

2 

5 

9 

14 

22 

35 

45 

56 

71 

90 






100 

1 

5 

8 

12 

19 

31 

39 

49 

63 

80 

100 





125 

0 

5 

7 

12 

19 

31 

39 

49 

62 

77 

98 

125 




150 

00 

4 

7 

11 

18 

30 

37 

47 

59 

74 

94 

118 

150 



175 

000 

4 

6 

10 

17 

27 

34 

43 

54 

69 

87 

108 

138 

175 


225 

0000 

4 

7 

11 

17 

28 

35 

44 

56 

76 

89 

112 

141 

178 

225 

275 

300000 


6 

9 

15 

24 

30 

38 

48 

61 

77 

96 

122 

154 

194 

325 

400000 


5 

8 

13 

21 

26 

33 

43 

54 

68 

85 

109 

137 

172 

400 

500000 


5 

8 

13 

21 

26 

33 

42 

53 

67 

84 

106 

134 

169 






Other 

Insulations 






Amps. B&S. 

14 

12 

10 

8 

6 

5 

4 

3 

2 

1 

0 

00 . 

000 

0000 

20 

14 

20 














25 

12 

15 

25 













30 

10 

11 

19 

30 












50 

8 

12 

19 

31 

50 











70 

6 

10 

17 

27 

44 

70 










80 

5 

10 

16 

25 

40 

64 

80 









90 

4 

10 

16 

25 

40 

64 

80 

90 








100 

3 

7 

12 

19 

31 

50 

63 

80 

100 







125 

2 

7 

12 

19 

31 

50 

63 

78 

99 

125 





150 

1 

7 

11 

18 

29 

47 

59 

74 

94 

118 

1150 





200 

0 

7 

12 

19 

31 

49 

62 

79 

99 

125 157 

200 




225 

00 

7 

11 

17 

28 

44 

56 

70 

89 

' 112 141 

178 

225 



275 

000 

6 

10 

17 

27 

43 

54 

68 

86 

1109 137 

173 

218 

275 


325 

0000 

6 

10 

16 

25 

40 

51 

64 

81 102 128 

1162 

204 

258 

325 

400 

300000 

5 

8 

14 

22 

35 

44 

55 

7C 

1 88 112 

; 140 

177 

223 

282 

500 

400000 

5 

8 

13 

20 

33 

41 

52 

66 

! 83 104 

132 

166 

209 

264 

600 

500000 

5 

8 

12 

20 

31 

40 

50 

63 

80 100 

127 

160 

202 

255 


ELECTRICAL TABLES AND DATA 


285 


TABLE C 

Table for determining total wattage required for 
incandescent lamps or other devices usually rated in 
watts. 

To find total wattage add all numbers found where 
lines pertaining to number of lamps and wattage of 
same cross. 

Number 


of 

lamps 1000 

750 

"Watts 
500 250 

150 

100 

60 

40 

25 

2 

2000 

1500 

1000 

500 

300 

200 

120 

80 

50 

3 

3000 

2250 

1500 

750 

450 

300 

180 

120 

75 

4 

4000 

3000 

2000 

1000 

600 

400 

240 

160 

100 

5 

5000 

3750 

2500 

1250 

750 

500 

300 

200 

125 

6 

6000 

4500 

3000 

1500 

900 

600 

360 

240 

150 

7 

7000 

5250 

3500 

1750 

1050 

700 

420 

280 

175 

8 

8000 

6000 

4000 

2000 

1200 

800 

480 

320 

200 

9 

9000 

6750 

4500 

2250 

2700 

900 

540 

360 

225 

10 

10000 

7500 

5000 

2500 

1500 

1000 

600 

400 

250 

15 

150Q0 

11250 

7500 

3750 

2250 

1500 

900 

600 

375 

20 

20000 

15000 

10000 

5000 

3000 

2000 

1200 

800 

500 

25 

25000 

18750 

12500 

6250 

3750 

2500 

1500 

1000 

625 

30 

30000 

22500 

15000 

7500 

4500 

3000 

1800 

1200 

750 

35 

35000 

26250 

17500 

8750 

5250 

3500 

2100 

1400 

875 

40 

40000 

30000 

20000 

10000 

6000 

4000 

2400 

1600 

1000 

45 

45000 

33750 

22500 

11250 

6750 

4500 

2700 

1800 

1125 

50 

50000 

37500 

25000 

12500 

7500 

5000 

3000 

2000 

1250 

55 

55000 

41250 

27500 

13750 

8250 

5500 

3300 

2200 

1375 

60 

60000 

45000 

30000 

15000 

9000 

6000 

3600 

2400 

1500 

65 

65000 

48750 

32500 

16250 

9750 

6500 

3900 

2600 

1625 

70 

70000 

52500 

35000 

17500 

10500 

7000 

4200 

2800 

1750 

75 

75000 

56250 

37500 

18750 

11250 

7500 

4500 

3000 

1875 

80 

80000 

60000 

40000 

20000 

12000 

8000 

4800 

3200 

2000 

85 

85000 

63750 

42500 

21250 

12750 

8500 

5100 

3400 

2125 

90 

90000 

67500 

45000 

22500 

13500 

9000 

5400 

3600 

2025 

100 

100000 

75000 

50000 

25000 

15000 

10000 

6000 

4000 

2500 

110 

110000 

82500 

55000 

27500 

16500 

11000 

6600 

4400 

2750 

120 

120000 

90000 

60000 

30000 

18000 

12000 

7200 

4800 

3000 

130 

130000 

92500 

65000 

32500 

19500 

13000 

7800 

5200 

3250 

140 

140000 

105000 

70000 

35000 

21000 

14000 

8400 

5600 

3500 

150 

150000 

112500 

75000 

37500 

22500 

15000 

9000 

6000 

3750 


286 


ELECTRICAL TABLES AND DATA 


TABLE Cl 


Table showing wattage capacity of different wires 



—110 Volts— 

—220 Volts— 

—440 Volts— 


Rubber 

Other 

Rubber 

Other 

Rubber 

Other 


Ins. 

Ins. 

Ins. 

Ins. 

Ins. 

Ins. 

14 

1650 

2200 

3300 

4400 

6600 

8800 

12 

2200 

2750 

4400 

5500 

8800 

1100G 

10 

2750 

3300 

5500 

6600 

11000 

13200 

8 

3850 

5500 

7700 

11000 

15400 

22000 

6 

5500 

7700 

11000 

15400 

22000 

30800 

5 

6050 

8800 

12100 

17600 

24200 

35200 

4 

7700 

9900 

15400 

19800 

30800 

39600 

3 

8800 

11000 

17600 

22000 

35200 

44000 

2 

9900 

13750 

19800 

27500 

39600 

55000 

1 

11000 

16500 

22000 

33000 

44000 

66000 

0 

13750 

22000 

27500 

44000 

55000 

88000 

00 

16500 

24750 

33000 

49500 

66000 

99000 

000 

19250 

30250 

38500 

60500 

77000 

121000 

0000 

24750 

35750 

49500 

71500 

99000 

143000 

200000 

22000 

33000 

44000 

66000 

88000 

132000 

300000 

30250 

44000 

60500 

88000 

121000 

176000 

400000 

35750 

55000 

71500 

110000 

143000 

220000 

500000 

44000 

66000 

88000 

132000 

176000 

264000 


If system is balanced use columns 220 volts for 
3-wire 110-volt systems and column 440 volts for 
3-wire 220 volt systems or for such voltages direct. 


Tables for calculating amperage of motors with 
various efficiencies, power factors systems and voltages. 

RULE FOR FINDING AMPERES 

In top part of table select numbers found where 
lines pertaining to efficiency and power factors cross 
and find same number in middle table. In same line 
under proper system will be found the number of 
amperes required for 1 H. P. at 110 volts. In bottom 
table select divisor pertaining to higher voltages, di¬ 
vide amperes by this and multiply by number of H. P. 
The result will give the total number of amperes re¬ 
quired. The efficiency of small motors is always much 
less than that of larger motors. 


ELECTRICAL TABLES AND DATA 287 


TABLE CII 


Power 

Factors 




Efficiency 




.95 .90 

.87* 

.85 

.82* 

.80 .75 

.70 

.65 .60 

.55 

.95 

.90 .86 

.83 

.81 

.78 

.76 .71 

.67 

.62 .57 

.53 

.90 

.86 .81 

.79 

.77 

.74 

.72 .68 

.63 

.59 .54 

.50 

.85 

.81 .77 

.74 

.72 

.70 

.68 .64 

.60 

.55 .51 

.47 

.80 

.76 .72 

.70 

.68 

.66 

.64 .60 

.56 

.52 .48 

.44 

.75 

.71 .68 

.66 

.64 

.62 

.60 .56 

.53 

.49 .45 

.41 

.70 

.67 .63 

.61 

.59 

.58 

.56 .53 

.49 

.46 .42 

.39 


Amperes for 1 H. 

P. at 110 Volts 



Direct 




Direct 




current 

Two 

Three 

current 

Two Three 


or s. phase phase 

phase 

or s. phase phase phase 

.39 

17.4 

12.5 

10.0 

.66 

10.3 

7.3 

5.9 

.41 

16.5 

11.9 


9.6 

.67 

10.1 

7.2 

5.9 

.42 

16.1 

11.6 


9.3 

.68 

9.9 

7.1 

5.8 

.44 

15.4 

11.1 


8.9 

.70 

9.7 

7.0 

5.6 

.45 

15.1 

10.8 


8.7 

.71 

9.6 

6.9 

5.5 

.46 

14.7 

10.5 


8.6 

.72 

9.5 

6.8 

5.4 

.47 

14.4 

10.3 


8.4 

.74 

9.2 

6.6 

5.3 

.48 

14.1 

10.2 


8.2 

.76 

8.9 

6.4 

5.1 

.49 

13.8 

9.9 


8.0 

.77 

8.8 

6.3 

5.1 

.50 

13.6 

9.7 


7.8 

.78 

8.7 

6.2 

5.0 

.51 

13.3 

9.5 


7.6 

.79 

8.6 

6.1 

5.0 

.52 

13.0 

9.4 


7.5 

.81 

8.4 

6.0 

4.8 

.53 

12.8 

9.2 


7.4 

.83 

8.2 

5.9 

4.7 

.54 

12.6 

9.0 


7.3 

.84 

8.1 

5.8 

4.6 

.55 

12.4 

8.8 


7.1 

.85 

8.0 

5.7 

4.6 

.56 

12.1 

8.7 


7.0 

.86 

7.9 

5.7 

4.5 

.57 

11.9 

8.5 


6.8 

.90 

7.5 

5.4 

4.3 

.58 

11.7 

8.4 


6.7 

.92 

7.4 

5.3 

4.3 

.59 

11.5 

8.3 


6.6 

.93 

7.3 

5.2 

4.2 

.60 

11.3 

8.1 


6.5 

.94 

7.2 

5.2 

4.2 

.61 

11.1 

8.0 


6.4 

.95 

7.1 

5.1 

4.1 

.62 

10.9 

7.8 


6.3 

.96 

7.0 

5.1 

4.1 

.63 

10.7 

7.7 


6.2 

.97 

7.0 

5.0 

4.0 

.64 

10.6 

7.6 


6.1 

.98 

6.9 

4.9 

4.0 





Voltages 





110 

220 

440 550 650 

1100 

2080 

2200 

Divisor 1 

2 

4 

5 

5.9 

11 

18.9 

20 


DIRECT CURRENT MOTORS 
TABLE CIII 


288 


ELECTRICAL TABLES AND DATA 


fcJD 

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cj 

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292 


ELECTRICAL TABLES AND DATA 


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To find the smallest wire permissible for a given motor load, find H. P. under proper voltage and 
insulation of wire; in same horizontal line under B. & S. will be found the gauge number of the wire 
to be used. 


ELECTRICAL TABLES AND DATA 


293 


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294 


ELECTRICAL TABLES AND DATA 


Tables for Calculating Drop in Voltage .—The drop 
in voltage in a direct current circuit is always equal to 
IR, while in an alternating current circuit it is equal 
to IZ. These formulae are, however, not well suited 
for use when the problem is to find the proper wire to 
be used where the loss is determined upon. 

That portion of the following tables devoted to 
direct currents consists simply of one column of fig¬ 
ures in which are given the conductances of the vari¬ 
ous wires. That part of the tables used for alternating 
current circuits gives the admittances of the various 
wires under different circumstances. The losses in 
voltage which form the basis of the following tables 
have been calculated from the formula: 


V[(Exp.f.) + {IR)] 2 +[(Exr.f.) + {IX) ] 2 =E 1 

where E stands for voltage to be delivered at end of 
line; p.f. for power factor of load; I for current in 
amperes; R for ohmic resistance of line; r./. for re¬ 
active factor; X for reactive volts in line, and E 1 for 
the e. m. f. necessary at the starting point to deliver E 
at the end of line. The ohmic resistance and the react¬ 
ive volts can be taken from Tables CIX and CX and 
the power factor (cosine of angle of lag) and reactive 
factor (sine of angle of lag) from Table CXI. To 
obtain the loss in volts it is necessary to subtract E 
from E 1 . Referring to Figure 34, which illustrates 
the common method of figuring drop in voltage for 
alternating current circuits, the losses for which the 
tables are calculated are equal to the difference be¬ 
tween the lines A and B. 

Having thus briefly outlined how the line losses, 
used as the basis of the following tables have been 
derived, we may now proceed to explain the tables and 
the method of their use. 



ELECTRICAL TABLES AND DATA 


293 


Since, according to a transposition of Ohms law, 

1 1 


E II 

— = Ii it follows that . In other words — 

i E K K 


or z 


give us the conductance or admittance which in con¬ 
nection with the current 1 will consume the voltage E. 
The numerical value of conductance or admittance in 
any line equals the number of amperes which can be 
transmitted over that line at a loss of one volt. This 
conductance for direct currents and admittance for 
alternating currents has been tabulated in the follow¬ 
ing pages. Hence, if we divide the current to be trans- 



Figure 34. 


mitted by the volts we wish to lose we shall obtain 
the value of the conductance or admittance which is 
necessary to cause this loss. The basis of the table is 
a line of 100 feet in length, which represents 200 feet 
of wire of a two-wire line. In order to find a wire 
which shall give us any desired loss, we need then 
merely to find what that loss is to be per 100 feet of 
line, and divide the amperes to be transmitted by this 
loss; then trace down the column describing the con¬ 
ditions (direct current or separation of wires) until 
we come to a number which about equals the one 
previously found. In connection with three-phase 
systems, if great accuracy is required, it will be neces¬ 
sary to divide the volts to be lost by 0.86 before pro¬ 
ceeding with the rest. 






296 


ELECTRICAL TABLES AND DATA 


In order to facilitate the calculations, the tables, 
CXII to CXIII, have been added. Table CXII gives 
the average value of amperes per H. P. with various 
voltages, and table CXIII shows the value in actual 
volts per hundred feet run of 1 per cent loss with the 
distances and voltages given. If the loss to be allowed 
over any distance and with any of the voltages given 
is stated in per cent, we need merely to multiply the 
number found where distance and voltage cross by 
the number of per cent to find the number of volts 
to be lost per 100 feet. 

Example: We have 50 H. P., three-phase, 60 
cycles, at 1000 volts, to transmit a distance of 2200 
feet, with 24-inch separation, at a loss of 5 per cent. 
What size of wire must be used? Fifty H.P. three 
phase at 1000 volts equals 35 amperes. (See Table 
CXII.) For a voltage of 1000 and a distance of 2200 
feet the number with which we must divide our cur¬ 
rent for one per cent is .451. (See Table CXIII.) 

This multiplied by the percentage of loss, 5 = 2.255, 
and this, in turn, divided by 0.86, gives us 2.62, with 
which we divide our amperes, 35, and obtain 13.3 as 
the admittance required. Tracing downward in table 
CXIV under the proper separation, 24 inches, we 
find the number 14.2 as the nearest, and this indicates 
a No. 5 wire. The same plan is used for direct cur¬ 
rent, and the conductances are given in column D. C. 
If larger wires are indicated, the conductances of the 
larger wire are in proportion to the circular mils for 
direct current. 


ELECTRICAL TABLES AND DATA 


297 


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298 


ELECTRICAL TABLES AND DATA 



rH O 

rH 03 (M Cd b* rH 
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0 0 0 0*00 


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o o o o o o 
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r—I I—I 1 —I rH O O 

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d o’ d o’ o’ d 


oooiocohO) biocoHoo) 

CO 05 N (M eg r-1 rlHHHnO 


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CO ‘O rH rH rH CO CO 

o o o o o o o 

o o o o o © © 

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to in M 05 H O 05 
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o o o o o o 


OOOOOO OOOOOO 


o o O O o o o 


05 100inH05 CO tH eg o oo to 
rH rH rH CO CO (M CM W W 55 H rl 

o rIHHrlrI r-l r-I H rH r-I i—I r-I 

to o O O O O O OOOOOO 


CO b- © b- CO lO 
rH i—I O O O O 


OOOOOO 


CO CM O 05 CO b» O 
O O O 05 05 05 05 
r— I rH i—I o O O O 

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ELECTRICAL TABLES AND DATA 


299 


TABLE CXI 


Power and Reactive Factors for Different Angles of Lag or 

Lead 



m 

t- 

-e 


m 

u 

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TO 

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bo 

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o 

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o 

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31 

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61 

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2 

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32 

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62 

.469 

.883 

3 

.998 

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33 

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63 

.454 

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4 

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34 

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64 

.438 

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5 

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35 

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65 

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.906 

6 

.994 

.105 

36 

.809 

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66 

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7 

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.122 

37 

.798 

.602 

67 

.391 

.921 

8 

.990 

.139 

38 

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.616 

68 

.375 

.927 

9 

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.156 

39 

.777 

.629 

69 

.358 

.934 

10 

.985 

.174 

40 

.766 

.643 

70 

.342 

.940 

11 

.982 

.191 

41 

.755 

.656 

71 

.326 

.946 

12 

.978 

.208 

42 

.743 

.669 

72 

.309 

.951 

13 

.974 

.225 

43 

.731 

.682 

73 

.292 

.956 

14 

.970 

.242 

44 

.719 

.695 

74 

.276 

.961 

15 

.966 

.259 

45 

.707 

.707 

75 

.259 

.966 

16 

.961 

.276 

46 

.695 

.719 

76 

.242 

.970 

17 

.956 

.292 

47 

.682 

.731 

77 

.225 

.974 

18 

.951 

.309 

48 

.669 

.743 

78 

.208 

.978 

19 

.946 

.326 

49 

.656 

.755 

79 

.191 

.982 

20 

.940 

.342 

50 

.643 

.767 

80 

.174 

.985 

21 

.934 

.358 

51 

.629 

.777 

81 

.156 

.988 

22 

.927 

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52 

.616 

.788 

82 

.139 

.990 

23 

.920 

.391 

53 

.602 

.799 

83 

.122 

.992 

24 

.914 

.407 

54 

.588 

.809 

84 

.105 

.994 

25 

.906 

.423 

55 

.574 

.819 

85 

.087 

.996 

26 

.899 

.438 

56 

.560 

.829 

86 

.070 

.997 

27 

.891 

.454 

57 

.545 

.839 

87 

.052 

.998 

28 

.883 

.470 

58 

.530 

.848 

88 

.035 

.999 

29 

.875 

.485 

59 

.515 

.857 

89 

.017 

.999 

30 

.866 

.500 

60 

.500 

.866 





Table Showing Average Amperage Per H. P. or K. W. with Various Systems and Voltages 

of Transmission 

Direct Current Single Phase Two Phase 4 Wire Two Phase 3 Wire Three P’nas'* 

Volts H.P. K-W. H.P. K.W. H.P. K.W. H.P. K.W. H.P. K.W. 


30 0 


ELECTRICAL TABLES AND DATA 


LO CO rH H Ci 
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ELECTRICAL TABLES AND DATA 


301 


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ELECTRICAL TABLES AND DATA 


305 


Economy of Conductors .—Any system of electrical 
conductors may be designed with reference to any of 
the following conditions: 

1. The conductors may be designed for minimum 
first cost, regardless of waste or quality of service. 

2. The conductors may be designed for the best 
possible service regardless of cost. 

3. The conductors may be designed for a minimum 
cost of generating plant. 

4. The conductors may be designed for maximum 
general economy of operation and installation; i. e., 
to yield the most profitable results in the long run. 

5. The conductors may be designed for a minimum 
first cost of generating plant and conductors. 

The first problem is solved by selecting the smallest 
wire allowed, either by heating limitations, or mechan¬ 
ical considerations. 

The second problem is solved by selecting very large 
wires, thus reducing the loss to any desired minimum. 

The third condition is fulfilled by selecting such 
large wires that the generator will not be called upon 
to deliver much waste power. 

The fourth problem has heretofore required some 
very extensive and elaborate calculations, but with the 
tables following, these have been reduced to a 
minimum and can be made in a few moments. This 
is, moreover, a subject which has been very much 
neglected, especially in connection with short runs 
such as are used inside of buildings, or to connect one 
building with another. The general practice has been 
to figure on a loss of from 2 to 5 per cent, or to dis¬ 
regard all question of economy and work from the 
standpoint of minimum first cost entirely. 

It must be understood that a certain loss in elec¬ 
trical transmission is unavoidable, and that the nearer 
we approach to an efficiency of 100 per cent the. more 
copper proportionately will be required to reduce the 


30G 


ELECTRICAL TABLES AND DATA 


remaining loss. For instance, if we have a certain 
wire causing a loss of 10 per cent, by adding another 
wire just like it we reduce our loss to 5 per cent; by 
adding two more similar wires we reduce the loss only 
2J per cent more, and by adding four more wires of 
the same size we gain only 1^ per cent more. In 
other words, the original wire was capable of trans¬ 
mitting 90 per cent of our energy; two wires 95 per 
cent, four w T ires 97| per cent, and eight w T ires 98j per 
cent. That under such circumstances it is easy to 
spend more in trjdng to save the energy than it is 
wrnrth, is evident. It has been shown by Sir Wm. 
Thompson and others that the most economical loss is 
that at which the annual value of the energy lost 
equals the interest charge on the cost of line construc¬ 
tion necessary to save it. In making calculations on 
this subject we need have nothing to do with the total 
length of line, or even the total cost of the line; we 
need be concerned only with the difference in cost 
between installing any convenient length of the small¬ 
est wire permissible, and that of substituting a larger 
wire. In some cases this may cause no other expense 
except that of the larger wire, in other cases it may be 
necessary to reconstruct the whole line in order to 
make room for larger wires. 

The basis of the following tables is found in the 
proposition and formula below: 


( 



R 


1000 x c 


the maximum capital which may economically be 
invested to substitute a larger wire in place of the 
smallest permissible wire where: 

R equals the resistance of the smallest wire con- 
sidered, 

r the resistance of the larger wire to be considered, 




ELECTRICAL TABLES AND DATA 


307 


c the interest rate applicable (governed by the num¬ 
ber of years line is to remain in use), 

I the current to be transmitted, 

p the rate per K. W. and 

h the number of hours I is used per year. 

In connection with this formula we need not con¬ 
sider the whole length of line, but may take any con¬ 
venient portion of it; therefore, in these tables a run 
of 100 feet (200 feet of wire) is taken as the basis of 
all calculations. 

The rate of interest applicable in this formula is 
the following: If line is to be in use only one year it 
must pay a dividend of 106 per cent; two years, 56; 
three years, 40; four years, 32; five years, 27; six 
years, 24; seven years, 21|; eight years, about 20, and 
nine years, 18f per year. 

In table CXVIII the values have been calculated for 
all of the wire sizes given, / 2 can be easily calculated 
and p and h can be found, for many values thereof, 
in table CXIX. The figures in table CXVIII have all 
been carried out to seven decimal points in order to 
simplify the comparison of small wires with the larger 
ones, and also to obtain greater accuracy. In most 
cases, however, when comparing small wires, it will 
not be necessary to use the full figures, and one or 
more figures at the right may be dropped. 

In using the tables it will be best to first find the 
quantity (Z 2 xpx/i), as this is fixed in any given 
problem. Next determine the smallest wire permis¬ 
sible, either on account of safety rules, mechanical 
considerations, or perhaps because it is already in¬ 
stalled. Note the number given in horizontal line in 
which the B & S gauge number is found and under 
the column pertaining to the number of years line is 
to remain in service; from this number subtract the 
corresponding number pertaining to some larger wire 
and with the remainder multiply the quantity I p h 


308 


ELECTRICAL TABLES AND DATA 


previously determined. This will give us the sum in 
dollars which may economically be invested to substi¬ 
tute the larger wire in place of the smaller. Bear in 
mind that this is only for a length of run of 100 feet. 
Example: We wish to find whether it will be profit¬ 
able to substitute a No. 6 wire in place of a No. 14 
carrying a load of 15 amperes, the rate per K. W. 
being 3 cents, the current to be used 1000 hours per 
year, and the line assumed to remain in use five 
years, at the end of which time it will be worthless. 
Three cents times 1000 hours gives us $30.00; 
this multiplied by 225 (I 2 ) gives us 6750. We now 
subtract .0002944 (No. 6) from .0018229 (No. 14), 
which leaves us (omitting the last three decimals) 
.0016; multiplying 6750 by this, we have 10.8, which 
is the number of dollars we may spend to install a 
No. 6 instead of a No. 14 wire. The difference in 
cost between a No. 14 and a No. 6 is from about ten 
to twelve dollars, not figuring the cost of supports. 

The foregoing calculations are assumed to be made 
from the standpoint of an engineer who connects onto 
an established system and who is responsible only for 
the actual loss in watts occurring on his part of the 
line. Sometimes, however, a line must be laid out 
from the central station, and the point then is not 
only the wattage loss, but also the loss in generator 
capacity. In this connection the length of the line 
is the principal consideration, and it becomes a ques¬ 
tion whether it is cheaper to provide a certain excess 
capacity in the generator and allow this to be lost 
in a small transmission line, or to provide a heavier 
line and use the generator pressure more economically. 
In lines of this character boosters are usually resorted 
to to regulate the pressure. 

The standard central station system usually soon 
evolves into an interconnected system of wires in 
which no accurate calculations on loss can be made. 


ELECTRICAL TABLES AND DATA 


309 


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ELECTRICAL TABLES AND DATA 


311 


TABLE CXX 
Copper Wire Table 

Bureau of Standards, Washington, D. C. 


I 

1 


i 


Working Table, International Standard Annealed Copper 
American Wire Gauge (B. & S.) 


Diam. ,-Cross Section-^ r-Ohms per 1000 Feet—\ Pounds 


Gauge 

i in 

Circular 

Square 

25° C 

65° C 

per 

No. 

Mils 

Mils 

Inches 

(=77° F) 

(=149° F) 

1000 Feet 

0000 

460. 

212 000. 

0.166 

0.0500 

0.0577 

641. 

000 

410. 

163 000. 

.132 

.0630 

.0727 

508. 

00 

365. 

133 000. 

.105 

.0795 

.0917 

403. 

0 

325. 

106 000. 

.0829 

.100 

.116 

319. 

1 

289. 

83 700. 

.0657 

.126 

.146 

253. 

2 

258. 

66 400. 

.0521 

.159 

.184 

201 . 

3 

229. 

52 600. 

.0413 

.201 

.232 

159. 

4 

204. 

41 700. 

.0328 

.253 

.292 

126. 

5 

182. 

33 100. 

.0260 

.319 

.369 

100 . 

6 

162. 

26 300. 

.0206 

.403 

.465 

79.5 

7 

144. 

20 800. 

.0164 

.508 

.586 

63.0 

8 

128. 

16 500. 

.0130 

.641 

.739 

50.0 

9 

114. 

13 100. 

.0103 

.808 

.932 

39.6 

10 

102 . 

10 400. 

.008 15 

1.02 

1.18 

31.4 

11 

91. 

8230. 

.006 47 

1.28 

1.48 

24.9 

12 

81. 

6530. 

.005 13 

1.62 

1.87 

19.8 

13 

72. 

5180. 

.004 07 

2.04 

2.36 

15.7 

14 

64. 

4110. 

.003 23 

2.58 . 

2.97 

12.4 

15 

57. 

3260. 

.002 56 

3.25 

3.75 

9.86 

16 

51. 

2580. 

.002 03 

4.09 

4.73 

7.82 

17 

45. 

2050. 

.001 61 

5.16 

5.96 

6.20 

18 

40. 

1620. 

.001 28 

6.51 

7.51 

4.92 

19 

36. 

1290. 

.001 01 

8.21 

9.48 

3.90 

20 

32. 

1020 . 

.000 802 

10.4 

11.9 

3.09 

21 

28.5 

810. 

.000 636 

13.1 

15.1 

2.45 




312 


ELECTRICAL TABLES AND DATA 


TABLE CXX—Continued 



Diam. 

f -Cross 

Section- n 

^Ohms per 1000 Feet--, 

Pounds 

Gauge 

No. 

in 

Mils 

Circular 

Mils 

Square 

Inches 

25° C 
(=77° F) 

65“ C 
(—149° F) 

per 

1000 Feet 

22 

25.3 

642. 

.000 505 

16.5 

19.0 

1.94 

23 

22.6 

509. 

.000 400 

20.8 

24.0 

1.54 

24 

20.1 

404. 

.000 317 

26.2 

30.2 

1.22 

25 

17.9 

320. 

.000 252 

33.0 

38.1 

0.970 

26 

15.9 

254. 

.000 200 

41.6 

48.0 

.769 

27 

14.2 

202. 

.000 158 

52.5 

60.6 

.610 

28 

12.6 

160. 

.000 126 

66.2 

76.4 

.484 

29 

11.3 

127. 

.000 099 5 

83.4 

96.3 

.384 

30 

10.0 

101. 

.000 078 9 

105. 

121. 

.304 

31 

8.9 

79.7 

.000 062 6 

133. 

153. 

.241 

32 

8.0 

63.2 

.000 049 6 

167. 

193. 

.191 

33 

7.1 

50.1 

.000 039 4 

211. 

243. 

.152 

34 

6.3 

39.8 

.000 031 2 

266. 

307. 

.120 

35 

5.6 

31.5 

.000 024 8 

335. 

387. 

.0954 

36 

5.0 

25.0 

.000 019 6 

423. 

488. 

.0757 

37 

4.5 

19.8 

.000 015 6 

533. 

616. 

.0600 

33 

4.0 

15.7 

.000 012 3 

673. 

776. 

.0476 

39 

3.5 

12.5 

.000 009 8 

848. 

979. 

.0377 

40 

3.1 

9.9 

.000 007 8 

1070. 

1230. 

.0299 


Note. 1.—The table is based on the international standard 
of resistance for copper, -which takes the fundamental mass 
resistivity = 0.15328 ohm (meter, gram) at 20° C, the corre¬ 
sponding temperature coefficient = 0.00393 at 20° C, and the 
density = 8.89 gi'ams per cc at 20° C. The temperature 
coefficient is proportional to the conductivity, whence the 
change of mass resistivity per degree C is a constant, 
0.000597 ohm (meter, gram). 

Note 2.—The values given in the table are only for an¬ 
nealed copper of the standard resistivity. The user of the 
table must apply the proper correction for copper of any 
other resistivity. Hard-drawn copper may be taken as about 
2.7 per cent higher resistivity than annealed copper. 

Note 3.—Ohms per mile, or pounds per mile, may be ob¬ 
tained by multiplying the respective values above by 5.28. 

Note 4.—For complete tables and other data see Circular 
No. 31 of the Bureau of Standards. 

Bureau of Standards, Washington, D. C., 1914 




ELECTRICAL TABLES AND DATA 


313 





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316 


ELECTRICAL TABLES AND DATA 


TABLE CXXII 

Aluminum Company of America 
Stranded Aluminum Wire 
Diameter and Properties 

Conductivity at 62 in the Matthiessen Standard Scale 

DIAMETERS WEIGHT IN POUNDS 

Triple Braid Resistance 


Number 
B. & S. 
Gauge 

Circular 

Mils. 

Decimal 
Parts 
of an 
Inch. 

Nearest 
32nd 
of an 
Inch. 

BARE Insulated 
Per Per 

1000 -Per 1000 

Feet. Mile. Feet. 

in Ohms, 
at 70° F 
per 

1000 Ft 

4 • • • 

1000000 

1.152 

1^2 

920. 

4858. 

1406. 

.016726 


950000 

1.125 

n 

874. 

4617. 

1337. 

.017606 


900000 

1.092 

1 tfz 

828. 

4374. 

1268. 

.018585 


850000 

1.062 

lf& 

782. 

4131. 

1199. 

.019679 


800000 

1.035 

l^J 

736. 

3888. 

1129. 

.020907 


750000 

.996 

1 

690. 

3645. 

1060. 

.022301 


700000 

963 

H 

644. 

3402. 

990. 

.023894 


650000 

.928 

*» 

598. 

3159. 

921. 

.025734 


600000 

.891 

§§ 

552. 

2916. 

852. 

.027878 


550000 

.854 

n 

506. 

2673. 

782. 

.030411 


500000 

.814 


460. 

2430. 

713. 

.033450 


450000 

.772 

§§ 

414. 

2187. 

644. 

* .037170 


400000 

.725 

ii 

368. 

1944. 

575. 

.041818 


350000 

.679 

\h 

322. 

1701. 

506. 

.047789 


300000 

.621 

ft 

276. 

1458. 

436. 

.055755 

• • • • 

250000 

.567 

& 

230. 

12.15 

366. 

.066905 

oooo 

211600 

.522 

n 

195. 

1028. 

313. 

.079045 

000 

167805 

.464 

u 

155. 

816. 

253. 

.099675 

00 

133079 

.414 

ii 

123. 

647. 

204. 

.12569 

0 

105534 

.368 

§ 

97. 

513. 

165. 

.15849 

1 

83694 

.328 

ii 

77. 

407. 

135. 

.19984 

0 

imJ 

66373 

.291 

$2 

61. 

323. 

112. 

.25200 

3 

52634 

.261 

i 

48.5 

256. 

93.5 

.31779 

4 

41742 

.231 


38.5 

203. 

76.5 

.40069 

5 

33102 

.206 

3 ? 2 

30.2 

161. 

56.0 

.50530 

6 

26250 

.180 

Yc 

24.1 

128. 

47.0 

.63720 







ELECTRICAL TABLES AND DATA 


31? 


TABLE CXXIII 


Aluminum Company of America 

Weight of Aluminum, Wrought Iron, Steel, Copper and Brass 

Wire. 


Diameters determined by American (Brown & Sharpe) Gauge. 
Water at 62° Fahrenheit, 62.355 lbs. per cubic foot. 

Drawn Wrought Iron is 2.8724 times heavier than Drawn Aluminum. 

“ Steel " 2.9322 “ 

“ Copper “ 3.3321 “ 

*' Brass “ 3.1900 " 

Weight of Wire per 1000 Lineal Feet 

No. Size of Ft. per lb. 


of each 
Gauge No. 

Inch 

Alumi¬ 

num 

Feet 

Alumi¬ 

num 

Lbs. 

Wro’t 

Iron 

Lbs. 

Steel 

Lbs. 

Copper 

Lbs. 

Brass 

Lbs. 

3000 

.46000 

5.185 

192.86 

553.97 

565.50 

642.68 

615.21 

000 

.40964 

6.539 

152.94 

439.33 

448.45 

509.32 

487.92 

00 

.36480 

8.246 

121.28 

348.40 

355.65 

404.20 

386.94 

0 

.32486 

10.396 

96.18 

276.30 

282.02 

320.50 

306.83 

1 

.28930 

13.108 

76.29 

219.11 

223.68 

254.20 

243.35 

o 

Li 

.25763 

16.529 

60.50 

173.78 

177.38 

201.60 

192.98 

3 

.22942 

20.846 

47.97 

137.80 

140.67 

159.86 

153.02 

4 

.20431 

26.281 

38.05 

109.28 

111.57 

126.78 

121.37 

5 

.1S194 

33.146 

30.17 

86.68 

88.46 

100.54 

96.26 

6 

.16202 

41.789 

23.93 

68.73 

70.15 

79.72 

76.32 

7 

.14428 

52.687 

18.98 

54.43 

55.56 

63.23 

60.53 

8 

.12849 

66.445 

15.05 

43.23 

44.12 

50.14 

48.00 

9 

.11443 

83.822 

11.93 

34.28 

34.99 

39.77 

38.07 

10 

.10189 

105.68 

9.462 27.18 

27.74 

31.53 

30.18 

11 

.090742 

133.24 

7.505 21.56 

22.01 

25.01 

23.94 

12 

.080808 

168.01 

5.952 17.10 

17.46 

19.83 

18.99 

13 

.071961 

211.86 

4.720 13.56 

13.84 

15.73 

15.06 

14 

.064084 

267.17 

3.743 10.75 

10.98 

12.47 

11.94 


318 


ELECTRICAL TABLES AND DATA 


TABLE CXXIII—Continued 


Size of 
No. each 

of No. 

Gauge Inch 

Ft. per lb. 
Alumi¬ 
num 

Feet 

r- Weight of Wire per 1000 Lineal Feet—. 
Alumi- Wro’t 

num Iron Steel Copper Brass 
Lbs. Lbs. Lbs. Lbs. Lbs. 

15 

.057068 

336.93 

2.968 

8.526 

8.704 

9.890 

9.468 

16 

.050820 

424.81 

2.354 

6.761 

6.903 

7.843 

7.508 

17 

.045257 

535.62 

1.867 

5.362 

5.474 

6.220 

5.955 

18 

.040303 

675.67 

1.480 

4.252 

4.342 

4.933 

4.723 

19 

.035890 

851.79 

1.174 

3.372 

3.443 

3.912 

3.755 

20 

.031961 

1074.11 

.9310 

2.672 

2.730 

3.102 

2.970 

21 

.028462 

1356. 

.7382 

2.121 

2.165 

2.460 

2.355 

22 

.025347 

1707.94 

.5855 

1.682 

1.717 

1.951 

1.868 

23 

.022571 

2153.78 

.4643 

1.333 

1.361 

.547 

1.481 

24 

.020100 

2715.91 

.3682 

1.058 

1.080 

1.227 

1.175 

25 

.017900 

3424.66 

.2920 

.8388 

.8563 

.9731 

.9316 

26 

.015940 

4317.78 

.2316 

.6652 

.6791 

.7716 

.7387 

27 

.014195 

5446.63 

.1836 

.5276 

.5385 

.6120 

.5858 

28 

.012641 

6868.13 

.1456 

.4183 

.4270 

.4853 

.4645 

29 

.011257 

8657.5 

.1155 

.3317 

.3386 

.3849 

.3683 

30 

.010025 

10917.0 

.0916 

.2631 

.2686 

.3052 

.2922 

31 

.008928 

13762.8 

.0727 

.2087 

.2130 

.2421 

.2318 

AO 

«_/ —4 

.007950 

17361.1 

.0576 

.1655 

.1693 

.1919 

.1837 

33 

.007080 

21886.7 

.0457 

.1312 

.1340 

.1522 

.1457 

34 

.006304 

27622. 

.0362 

.1040 

.1062 

.1207 

.1155 

35 

.005614 

34807.3 

.0287 

.0825 

.0842 

.0957 

.0916 

36 

.005000 

43878.9 

.0228 

.0655 

.0668 

.0759 

.0727 

37 

.004453 

55245. 

.0181 

.0519 

.0530 

.0602 

.0577 

38 

.003965 

69783.7 

.0143 

.0413 

.0420 

.0478 

.0457 

39 

.003531 

88028.2 

.0114 

.0326 

.0333 

.0379 

.0363 

40 

.003144 

110980. 

.0090 

.0259 

.0264 

.0300 

.0287 

Specific gravity Wire... 

2.680 

7.698 

7.858 

8.930 

8.549 


Wt., per cu. ft., Wire.. 167.111 480.000 490.000 556.830 533.073 


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ELECTRICAL TABLES AND DATA 




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323 


Comparative Weights of Copper Clad and Copper Weatherproof Wire. 


324 ELECTRICAL TABLES AND DATA 

TABLE CXXVII 


18% German Silver Resistance Wire. 


No. 

B. & S. Diam. 
Gauge Ins. 

0 .325 

1 .289 

2 .258 • 

3 .229 

4 .204 

5 .182 

Area 

C. M. 

105,625 

83,521 

66,564 

52,441 

41,616 

33,124 

Weight 

Resistance Lbs. 
per per 

1000 Ft. 1000 Ft. 
at 75° F. Bare 

1.95 302 

2.53 239 

3.22 190 

4.14 150 

5.18 119 

6.55 95 

Ohms 
Per Ltx 

.00645 

.01025 

.0163 

.0259 

.0412 

.0656 

6 

.162 

26,244 

8.28 

72 

.1042 

7 

.144 

20,736 

10.47 

59 

.1657 

8 

.128 

16,384 

13.22 

47 

.2635 

9 

.114 

12,996 

16.68 

37.6 

.4189 

10 

.102 

10,404 

20.8 

29.2 

.6663 

11 

.091 

8,281 

26.2 

23.7 

1.059 

12 

.081 

6,561 

33.2 

18.8 

1.684 

13 

.072 

5,184 

42 

14.8 

2.619 

14 

.064 

4,096 

53 

11.7 

4,258 

15 

.057 

3,249 

67 

9.3 

6.773 

16 

.051 

2,601 

84 

7.45 

10.768 

17 

.045 

2,025 

107 

5.73 

17.121 

18 

.040 

1,600 

136 

4.57 

27.216 

19 

.036 

1,296 

168 

3.7 

43.281 

20 

.032 

1,024 

222 

2.93 

68.838 

21 

.0285 

812.3 

270 

2.32 

109.45 

22 

.0253 

640.1 

340 

1.83 

174.03 

23 

.0226 

510.8 

425 

1.46 

276.78 

24 

.0201 

404.0 

540 

1.15 

439.95 

25 

.0179 

320.4 

680 

.91 

699.72 

26 

.0159 

252.8 

864 

.72 

1,112.4 

27 

.0142 

201.6 

1,076 

.58 

1,768.8 

28 

.0126 

158.8 

1,370 

.46 

2,811.9 

29 

.0113 

127.7 

1,700 

.365 

4,473 

30 

.010 

100.0 

2,180 

.286 

7,011 

31 

.0089 

79.2 

2,750 

.266 

11,306 

32 

.008 

64.0 

3,400 

.183 

17,980 

33 

.0071 

50.4 

4,300 

.144 

28,581 

34 

.0063 

39.7 

5,480 

.113 

45,465 

35 

.0056 

31.4 

6,920 

.090 

72,261 

36 

.005 

25.0 

8,700 

.071 

114,933 

37 

.0045 

20.2 

11,000 

.058 

182,742 

38 

.004 

16.0 

13,850 

.046 

291,270 

39 

.0035 

12.2 

17,550 

.035 

462,000 

40 

.003 

9.0 

22,200 

.026 

887,250 












ELECTRICAL TABLES AND DATA 


325 


The composition commonly known as German Silver is 
that containing 18% of nickel. Its resistance varies some¬ 
what in different lots, and according to temper, and is 
approximately 21 times that of copper. 

30% German Silver Wire has a resistance approximately 
28 times that of copper. 


TABLE CXXVIII 

Properties of Galvanized Telephone and Telegraph Wires. 
Based on Standard Specifications. 

American Steel and Wire Co. 


Size 

B.W.G. 

Diam. 
in Mils 

<- h Approximate 

wt. in lbs. 

^ S os Per Approximate 

£^<2 1000 Per breaking 

feet mile strain in lbs. 

Res. per mil® 
(Latent Ohms) 
at 68° F.. 20° C. 






Ex. 

B.B. 

B.B. 

Steel 

Ex. 

B.B. 

B.B. 

Steel 

0 

340 

115600 

313 

1655 

4138 

4634 

4965 

2.84 

3.38 

3.93 

1 

300 

90000 

244 

1289 

3223 

3609 

3867 

3.65 

4.34 

5.04 

2 

284 

80656 

218 

1155 

2888 

3234 

3465 

4.07 

4.85 

5.63 

3 

259 

67081 

182 

960 

2400 

2688 

2880 

4.90 

5.83 

6.77 

4 

238 

56644 

153 

811 

2028 

2271 

2433 

5.80 

6.91 

8.01 

5 

220 

48400 

131 

693 

1732 

1940 

2079 

6.78 

8.08 

9.38 

6 

203 

41209 

112 

590 

1475 

1652 

1770 

7.97 

9.49 

11.02 

7 

180 

32400 

87 

463 

1158 

1296 

1389 

10.15 

12.10 

14.04 

8 

165 

27225 

74 

390 

975 

1092 

1170 

12.05 

14.36 

16.71 

9 

148 

21904 

60 

314 

785 

879 

942 

14.97 

17.84 

20.70 

10 

134 

17956 

49 

258 

645 

722 

774 

18.22 

21.71 

25.29 

11 

120 

14400 

39 

206 

515 

577 

618 

22.82 

27.19 

31.55 

12 

109 

11881 

32 

170 

425 

476 

510 

27.65 

32.94 

38.23 

13 

95 

9025 

25 

129 

310 

347 

372 

37.90 

45.16 

52.41 

14 

83 

6889 

19 

99 

247 

277 

297 

47.48 

56.56 

65.66 

15 

72 

5184 

14 

74 

185 

207 

222 

63.52 

75.68 

87.84 

16 

65 

*€25 

11 

61 

152 

171 

183 

77.05 

91.80 

106.55 


326 


ELECTRICAL TABLES AND DATA 


TABLE CXXIX 

Approximate Outside Dimensions of Wires and Cables 

The table below is for the use of those who wish to esti¬ 
mate carrying capacities of conductors without cutting into 
insulation or shutting down a plant. The figures given are 
thought to be an average for voltage up to 600. Weather¬ 
proof dimensions are for minimum thickness allowed by 
N. E. C. 


Rubber Covered Weatherproof 


V 

13 

o 


(q 




v 



<D 


• 



Vi 

o 

B o 

® A 

a 

p p 

c$ 

O <D 

• 

(-> t- 

o 

• H 

A 

F ® 



V 




<U 

% 




H 

a> 

+■> 

0> 

a 

o 

® Pti 

a 

P 



at 

O 

O) 

. o 

V 

V 

•V> o 

• rH 

A 

• 

O 

a> 



2000000 2V S 7200 

1750000 2i/ 32 62% 4 6300 
1500000 1% 5B%4 5550 

1250000 1% 5S% 4 4700 

1000000 13% 4 45% 4 3900 
950000 13i/ 64 44% 4 3750 
900000 12% 4 43% 4 3575 
850000 12% 4 43<!f >4 3400 
8 0 0 0 00 12% 4 42 % 4 3250 
750000 12% 4 4i%4 3000 
700000 12% 4 4% 4 2850 
650000 li% 4 4i/ 64 2 835 
600000 li% 4 35% 4 2575 
550000 li% 4 347/ 64 2325 
500000 1% 4 33y 64 2130 
450000 1% 4 325/ 64 1 92 5 
400000 1% 4 3i% 4 1735 
350000 e% 4 36/ 64 1525 

300000 6% 4 25% 4 1360 

25 0000 57/ 64 25 i / 64 1185 

225000 $%4 24% 4 975 


156/ 64 557/ 04 7008 
H% 4 535^ 4 6190 
14%4 513/34 5375 
1 3 %4 4r>% 4 4500 
1 2 %1 427/ 64 3 6 75 

120/64 4%4 3330 

H6/ 64 359/ 64 3000 
11 % 4 36% 4 2800 
l 12 /64 34%4 2650 

1%4 335/ G4 2250 

1%4 325/ 64 1 9 00 
01/64 263/.4 1 700 
5%4 257/ 64 1 550 
5 %4 24%4 1350 
5%4 235/ 64 1175 
4 %4 228/ 64 985 


Lead Covered 

V 

<X> 

-4-> 

jh <35 

V 

<D 


a 

c3 

3 a 
o o 

t . . 

‘To 

• rH 

A 

645 

)0I 

LA 

2%4 

6 4 3/ 6 4 

11300 

2%4 

6 2 %4 

10225 

10%4 

f/64 

9100 

1 5 %4 

53 %4 

7950 

1 39 /g4 

6%4 

6280 

1 3 %4 

45 %4 

6050 

1 3 %4 

44%4 

5800 

1 3 %4 

4 4 6/ 6 4 

5580 

13 %4 

44%4 

5350 

1 2 %4 

4 3 3/64 

5110 

1 2 %4 

42 %4 

4880 

1 2 %4 

420/64 

4640 

1 2 %4 

41%4 

4385 

1 2 %4 

414/64 

4150 

H%4 

3 5 %4 

3480 

H%4 

34/64 

3225 

H%4 

34%4 

3000 

1%4 

3 2 % 4 

2750 

^Yca 

31/64 

2480 

0/64 

3 

2230 


ELECTRICAL TABLES AND DATA 


327 


TABLE CXXX 


Approximate Outside Diameter of Wires and Cables 
Rubber Covered, 0 to 600 Volts 


wt. per 


B . & S. 

- Solid - 

-Stranded- 

1000 



Duplex 




S.B. 

D.B. 

S.B. 

D.B. 

feet 

—Solid - 

-Stranded- 

0000 

4 %4 

47 /64 

4 %4 

52/ 64 

850 

4 %4 

X 

91 /64 

5 %4 

X 

°%4 

000 

4 %4 

4 %4 

4 %4 

4 %4 

700 

4 %4 

X 

8 %4 

48 /G4 

X 

9 %4 

00 

3 Mm 

4 %4 

41 /64 

44 / g 4 

575 

4 Mm 

X 

7 Mm 

44 /64 

X 

8 %4 

0 

3 %4 

3 Mm 

3 %4 

41 /G4 

475 

3 %4 

X 

71 /64 

4 Mg4 

X 

7 %4 

1 

3 %4 

3 %4 

3 %4 

3 %4 

375 

3 %4 

X 

6 %4 

3 %4 

X 

7 %4 

2 

2 %4 

3 Mm 

3 %4 

3 %4 

300 

31 &4 

X 

5 %4 

3 %4 

X 

6 %4 

3 

2 %4 

2 %4 

2 %4 

3 Mm 

260 

2 %4 

X 

54 /64 

3 M)4 

X 

5 %4 

4 

24 /G4 

27 /g4 

2 %4 

2 %4 

215 

2 %4 

X 

51 /g4 

3 %4 

X 

5 %4 

5 

23/ 64 

2 %4 

2 %4 

2 %4 

185 

2 %4 

X 

4 %4 

27 /64 

X 

5 %4 

6 

21 /64 

24 /64 

2 %4 

2 %4 

150 

2 %4 

X 

4 %4 

2 %4 

X 

4 %4 

8 

17 /64 

2 %4 

18 /64 

21 /G4 

100 

21 /64 

X 

31 /64 

22 /64 

X 

3 %4 

10 

15 /G4 

18 /64 

16 /64 

4 %4 

75 

4 %4 

X 

3 %4 

2 %4 

X 

3 %4 

12 

14 /64 

1 Mm 

16 /64 

*%4 

60 

17 /64 

X 

31 /64 

18 /64 

X 

3 %4 

14 

J %4 

16 /G4 

14 /64 

17 /64 

45 

16 / g 4 

X 

2 %4 

17 /64 

X 

?%4 

16 

10 /64 

13 /64 



30 

*%4 

X 

2 %4 




18 

%4 

12 / G4 



20 

*%4 

X 

2l /64 







600 

to 3500 Volts 






0000 

4 %4 

4 %4 

51 / g 4 

5 %4 

850 

5 %4 

X 

9 %4 

X 104/ 64 

000 

4 %4 

4 %4 

47 /64 

5 %4 

700 

4 %4 

X 

8 %4 

5 %4 

X 

9 764 

00 

3 %4 

4 %4 

4 %4 

4 %4 

575 

4 %4 

X 

8 Vg4 

4 %4 

X 

8 %4 

0 

37 /g4 

4 %4 

4 %4 

4 %4 

475 

4 %4 

X 

7 %4 

4 %4 

X 

8 7 X 64 

1 

3 %4 

37 /64 

37 /G4 

4 %4 

375 

3 %4 

X 

7 r 6 4 

4 %4 

X 

7 %4 

2 

3 %4 

3 %4 


300 

3 %4 

X 

6 %4 

3i /g4 

X 

71 /^4 

3 

3 %4 

3 %4 

34 /64 

37 /64 

260 

3 %4 

X 

6 M64 

3 %4 

X 

G Vg4 

4 

2 %4 

31 /G4 

3 %4 

3 %4 

215 

3 %4 

X 

5 %4 

3 %4 

X 

°%4 

5 

27 /64 

3 %4 

32 /64 

3 %4 

185 

3 %4 

X 

5 %4 

3 %4 

X 

5 %4 

6 

2 %4 

2 %4 

27 /64 

S0 /64 

150 

2 %4 

X 

5 %4 

3 %4 

X 

5 %4 

8 

2 %4 

2 %4 

2 %4 

27 / g 4 

100 

2 %4 

X 

4 %4 

2 %4 

X 

5 %4 

10 

22/ 64 

2 %4 

2 %4 

2 Mg4 

75 

2 %4 

X 

4 %4 

2 %4 

X 

4 %4 

• 12 

2 %4 

2 %4 

21 /64 

2 Mg4 

60 

2 %4 

X 

4 %4 

24 /64 

X 

44 /64 

14 

J %4 

2 %4 

2 %4 

2 %4 

45 

2 %4 

X 

41 /64 

2 %4 

X 

41 /g4 


Weights given are thought to be average weights; duplex 
wires weigh nearly double the amounts given. 


328 


ELECTRICAL TABLES AND DATA 


TABLE CXXXI 

Approximate Weight and Diameters of Rubber Covered Lead 

Encased Cables 


Single Conductor 0 to 600 Volts Duplex Conductor 


B.&S. 

Diameter 

Wt. per 

1000 ft. 

Diameter 

Wt. per 
1000 ft. 

0000 

5 %4 

1600 

5 %4 X 104/ 64 

2900 

000 

51 /64 

1400 

% X 9%4 

2600 

00 

4 %4 

1250 

4 %4 X 9% 4 

2300 

0 

4 %4 

1100 

% X 78/64 

2000 

1 

3 %4 

900 

s %4 X 6 %4 

1700 

2 

3 %4 

750 

3 %4 X 6 %4 

1400 

4 

2 %4 

500 

%X 56/ 64 

1100 

6 

2 %4 

400 

2 %4 X 5 %4 

800 

8 

2 %4 

300 

2 %4 X 4 %4 

600 

10 

21 /64 

275 

21 /64 X 38^ 4 

500 

12 

18 /64 

175 

19 /64 X 34/ 64 

350 

14 

16 /64 

150 

18 /64X 3% 4 

300 


ELECTRICAL TABLES AND DATA 


329 


TABLE CXXXII 


8ths. 

16ths. 

1 

32nds. 

64ths. 

| 

Mils. 

8ths. 

16ths. 

32nds. 

64ths. 

Mils. 




1 

15.6 


| 

33 

515.6 



1 

2 

31.2 



17 

34 

531.2 




3 

46.9 




35 

546.8 


1 

2 

4 

62.5 


9 

18 

36 

562.5 




5 

78.1 




37 

578.1 



3 

6 

93.7 



19 

38 

593.7 




7 

109.3 




39 

609.3 

1 

2 

4 

8 

125. 

5 

10 

20 

40 

625. 




9 

140.6 




41 

640. ft 



5 

10 

156.2 



21 

42 

656.2 




11 

171.8 




43 

671.8 


3 

6 

12 

187.5 


11 

22 

44 

687.5 




.. 13 

203.1 




45 

703.1 



7 

14 

218.7 



23 

46 

718.7 




15 

234.3 




47 

734.3 

2 

4 

8 

16 

250. 

6 

12 

24 

48 

750. 




17 

265.6 




49 

765 5 



9 

18 

281.2 



25 

50 

781.2 




19 

296.8 




51 

796.8 


5 

10 

20 

312.5 


13 

26 

52 

812.5 




21 

328.1 




53 

828.1 



ii.. 

22 

343.7 



27 

54 

843.7 




23 

359.3 




55 

859.3 

3 

6 

12 

24 

375. 

7 

14 

28 

56 

875. 




25 

390.6 




57 

890.6 



..13.. 

26 

406.2 



29 

58 

906.2 




27 

421.8 




59 

921.8 


7 

14 

28 

437.5 


15 

30 

60 

937.5 




23 

453.1 




61 

953.1 



.15.. 

30 

468.7 



31 

62 

968.7 




31 

484.3 




63 

984.3 

4 

8 

16 

32 

500. 

8 

16 

32 

64 

1000. 





















































































CARRYING CAPACITIES OF WIRES FOR SHORT PERI¬ 
ODS AND INTERMITTENT LOADS. 

The following tables of carrying capacities were 
prepared by the use of formulae deduced by the 
authors from heating curves of a large number of 
conductors experimentally determined in the labora¬ 
tories of the Commonwealth Edison Co. of Chicago. 
The tests were made at the suggestion of the Depart¬ 
ment of Gas and Electricity of the City of Chicago 
and in some of these tests the engineers of the above 
company were assisted by engineers of the city de¬ 
partment. A full description of these tests was given 
in the Electrical World during 1918. 

The data used in compiling the figures given were 
obtainable only in the form of “curves.’’ It is well 
known that such curves are to a large extent an inter¬ 
polation of values, and it is therefore quite unlikely 
that many of the values given would produce exactly 
the temperature assigned to them if subject to a test. 
A study of the curves showed that in a general way 
the temperature rise in any given conductor was pro¬ 
portional to the square of the current used, but there 
were also some exceptions, due probably to errors of 
observation and interpolation as well as to a variety 
of causes. 

In order to eliminate these errors as much as pos¬ 
sible, and at the same time provide a simple'means of 

330 


ELECTRICAL TABLES AND DATA 


331 


interpolation to determine the carrying capacity of 
euch wires as were not tested, the amperage necessary 
to bring each size of wire to a certain temperature was 
first computed. After this had been done, the circu¬ 
lar mils of the conductor were divided by the amper¬ 
age found, thus giving the circular mils per ampere. 

The circular mils per ampere of all the conductors 
tested were then plotted vertically, while the copper 
contents were laid out horizontally, and the whole 
combined in the form of a curve in the well known 
way. The final carrying capacity was then deter¬ 
mined by dividing the circular mils in the conductor 
by the circular mils per ampere indicated by the 
curve. It is believed that, in this manner, fairly ac¬ 
curate average values have been obtained. 

The current which will cause a given temperature 
rise in a conductor can be found by the following 
formula: 



in which T is the desired temperature; t the tempera¬ 
ture attained in the conductor by the current i and 
1 is the current to be found. This formula does not 
take into account the fact that the resistance of the 
conductor increases with the temperature, as this is 
considered negligible for all practical purposes. The 
values of t and i are given in the tables for rubber 
covered wires. Those conductors, in connection with 
which no temperature rises are given, were not tested, 
but the current values given were obtained by interpo¬ 
lation as before explained. 

The tables applying to conduits also give the di¬ 
mensions of the conduits used in the tests. Under 
the heading, “N. E. Code,” we give the amperage 



332 


ELECTRICAL. TABLES AND DATA 


allowed by the code. Under the heading, ‘ 4 Calculated 
Carrying Capacities,” we give those calculated as 
described above. These values must not be used in 
conflict with the official figures given by the code, as 
they are not yet sanctioned thereby. The amper¬ 
ages given under, “Short Time in Minutes,” are those 
which it is believed the various conductors can safely 
carry for the length of time given, provided no appre¬ 
ciable heating has been caused before this load is ap¬ 
plied. 

Four tables are given. Two of them are calculated 
for a temperature rise of 72 degrees Fahrenheit, and 
the other for 36 degrees Fahrenheit. They are also 
arranged for open and concealed wires, the latter in 
conduit. The three wires run in conduit were all 
carrying the same current and the heating effect there 
obtained will be exceeded only in cases where the 
four wires of a two-phase system are run in the same 
pipe. With the ordinary three-wire lighting system, 
the heating will be considerably less. 

The temperature of rubber covered wire should not 
exceed 120 degrees F. but that covered with other 
insulations may rise to 150 degrees, and asbestos cov¬ 
ered wires may be carried to higher temperatures 
than this. 

The following tables are intended to assist in the 
selection of the smallest conductor that may be used 
to carry an intermittent load. The ultimate tempera¬ 
ture rise of a conductor subject to an intermittent 
load depends upon the ratio between the “on” and 
“off” time of the current. Unless the current is off 
long enough to allow the loss of the heat accumulated 
during the “on” time, the temperature will rise. 

At low temperatures the dissipation of heat pro- 


ELECTRICAL. TABLES AND DATA 


333 


ceeds slowly, but at higher temperatures it is much 
more rapid. For this reason, the relative time in 
which a given quantity of heat, can be dissipated 
varies greatly with the temperature permitted. 

A separate table is provided for each size of wire 
considered; in conduit as well as for open wiring. 
•Each table is divided into two parts. In the left hand 
portion of the tables is given the time in seconds re¬ 
quired for the currents given at the top, under the 
heading, “Heating Load; Amperes,” to raise the tem¬ 
perature of the wire 5 degrees F. within the range of 
temperature given under the heading, “Temperature 
Range, ” in conduit or open wires as the case may be. 

Thus, referring to the table for No. 14 wire in con¬ 
duit, we see that a current of 25 amperes will produce 
a rise of 5 degrees, between the range of 47 and 52, 
in 220 seconds, but also that it will require 1,350 
seconds to effect a temperature rise from 67 to 72 in 
the same conductor by the same current. In this 
connection we need not pay any attention to the lower 
temperatures, as we are interested only as the critical 
temperatures are approached. 

If an intermittent load is continued long enough, 
there will be a steady rise in temperature until the 
point is reached at which the dissipation of heat equals 
the supply. Therefore, if we allow sufficient cooling 
time, we can keep the temperature within bounds. 

In the right hand portion of the tables we give the 
time in seconds required to dissipate the heat gen¬ 
erated during the time given in the same horizontal 
lines. 

Thus, again referring to the table for No. 14 wire, 
we see that with a temperature range of 22-27 degrees, 
the heat produced in 110 seconds requires 300 seconds 


334 ELECTRICAL TABLES AND DATA 

to cool off, while if we allow the temperature to go to 
57-62, that generated in 400 seconds will be lost in 
40 seconds. Cooling times are given with zero load 
as well as with continued loads of the amperages 
given. 

The temperature of rubber covered wire should not 
be allowed to rise above 120 degrees Fahrenheit, and 
that of ‘ ‘ Other Insulations ’ 9 should not go above 150 
degrees F. Asbestos covered wires, however, may be 
allowed to run much hotter. In order to facilitate the 
selection of the proper conductor there is.provided 
a column “ Limiting Outer Temperature. ’ 9 A sepa¬ 
rate column is provided for rubber covered and other 
insulation covered wires. The figures there given in¬ 
dicate that, in locations where the temperature of the 
air does not rise above the values given, the tempera¬ 
ture of the conductor may be allowed to rise to the 
value of the highest figure given in the same horizontal 
line under the heading *‘Temperature Range,” either 
in conduit or open wires. 

The simplest method of using the tables consists of 
first determining the limiting outer temperature. 
Next find the peak number of amperes and the length 
of time in seconds during which this amperage is 
used. Then proceed to find the minimum amperage 
and the length of time during which it is in. use. 
Make notes of these values and always estimate them 
with a view to obtaining the hardest operating condi¬ 
tions likely to occur. Now proceed to find the small¬ 
est wire under which the amperage in question is given 
and, selecting the horizontal line in which the limiting 
temperature is found, see whether the ratio of the on 
and off times corresponding to the temperature given 
is the same as that in the problem. 


ELECTRICAL. TABLES AND DATA 


335 


Example: We have a peak load of 80 amperes 
which lasts for 60 seconds and is then reduced to 25 
amperes for 200 seconds; this being the estimated 
regular cycle of operation of the circuit. Wires are in 
conduit. The smallest wire under which an amperage 
of 80 or more is found is a No. 8. Here we find, in 
the horizontal line pertaining to 83 degrees F., that 
105 amperes will cause a temperature rise of 5 degrees 
in 21 seconds and that this heat, even with only 1T V 2 
amperes in continued use, requires 285 seconds for 
its dissipation. This will not do, and we proceed to 
the next size of wire. Here we find, in the correspond- 
ing horizonal line, that 80 amperes will require 100 
seconds to raise the temperature of the wire 5 degrees, 
and that this heat will be lost in 300 seconds, even with 
25 amperes in continued use. Furthermore, as the 
cooling time is three times as long in this case, while 
in our problem it was three and one-third times as 
long, the wire thus found will not heat quite as much 
as indicated and will therefore be safe to use. 


336 


ELECTRICAL TABLES AND DATA 


Table CXXXII 
Wires in Conduit 

Table of Carrying Capacities; three conductors in conduit, 
each carrying same current. 

20° C.; 36° F. temperature rise above surrounding air. 

Use this table for rubber covered wires in conduit where 
temperature of air does not exceed 85° F., and for other 
insulations at temperatures from 85° F. to 125° F. 


B. & S. 
gauge. 

Size 

tonduit 

N. E. 

CODE 

Calculated Carrying Capacities 36° 

F. rise 

Carrying 

capacity 

amperes 

Temp, 
rise in 
deg. F 

Indefinite 

time 

amperes 

sap 

30 

luira ut 

15 

erarj Woq 

10 

S 

5 

14 

y 2 " 

15 

27.0 

17 

19 

22 

24 

30 

12 


20 

31.0 

22 

24 

26 

29 

35 

10 

%" 

25 

27.9 

27 

30 

35 

40 

45 

8 

i " 

35 

29.9 

36 

43 

50 

60 

65 

6 

i " 

50 

33.1 

52 

60 

73 

80 

105 

5 

• • • 

55 

• • • 

56 

69 

88 

100 

125 

4 

i%" 

70 

40.7 

64 

77 

97 

110 

140 

3 

1 V 4 " 

80 

34.9 

82 

93 

113 

135 

165 

2 

1 %" 

90 

34.7 

90 

106 

130 

155 

195 

1 

1V 2 " 

100 

39.1 

96 

126 

154 

180 

225 

0 

2 " 

125 

41.2 

110 

147 

182 

210 

275 

2/0 

2 " 

150 

41.8 

130 

179 

220 

260 

340 

3/0 

2 " 

175 

39.4 

150 

213 

270 

320 

420 

200000 

• • • 

200 

• • • 

175 

247 

310 

355 

480 

4/0 

2V 2 " 

225 

57.6 

180 

256 

325 

395 

515 

250000 

• • • 

240 

• • • 

205 

297 

375 

455 

585 

300000 

3 " 

275 

45.2 

238 

345 

435 

535 

690 

350000 

• • • 

300 

• • • 

265 

395 

500 

605 

790 

400000 

3 " 

325 

42.1 

290 

440 

555 

690 

850 

500000 

3 " 

400 

48.1 

345 

529 

660 

800 

1090 

600000 

• • • 

450 

• • • 

390 

610 

750 

915 

1225 

700000 

• • • 

500 

• • • 

430 

680 

830 

1025 

1400 

750000 

4 " 

525 

44.8 

450 

710 

870 

1080 

1450 

800000 

• . • 

550 

• • • 

465 

745 

905 

1120 

1525 

900000 

• • • 

600 

• • • 

495 

810 

975 

1210 

1665 

1000000 

4V 2 " 

650 

55.2 

525 

870 

1040 

1295 

1800 
































ELECTRICAL TABLES AND DATA 


337 


Table CXXXIII 
Wires in Conduit 

Table of Carrying Capacities; three conductors in conduit, 
each carrying same current. 

40° C.; 72° F. temperature rise above surrounding air. 

Use this table for “Other insulations” in conduit where 
temperature does not exceed 80° F., and for rubber covered 
wire where temperature of air does not exceed 50° F. 


B. & S. 
gauge, c 


n. e. 

CODE 

Slue 

onduit 

Carrying 

capacity 

amperes 

Temp 
rise ir 
deg. F 

i-- 

14 

y 2 " 

15 

27.0 

12 

%" 

20 

31.0 

10 

%" 

25 

27.9 

8 

i " 

35 

29.9 

6 

i " 

50 

33.1 

5 

• • • 

55 

• • • 

4 

l 1 /*" 

70 

40.7 

3 

1 %" 

80 

34.9 

2 

iy 2 " 

90 

34.7 

1 

iy 2 " 

100 

39.1 

0 

2 " 

125 

41.2 

2/0 

2 " 

150 

41.8 

3/0 

2 " 

175 

39.4 

200000 

• • • 

200 

• • • 

4/0 

2 y 2 " 

225 

57.6 

250000 

• • • 

240 

• • • 

300000 

3 " 

275 

45.2 

350000 

• • • 

300 

• • • 

40000(3 

3 " 

325 

42.1 

500000 

3 " 

400 

48.1 

600000 

... 

450 

• • • 

700000 


500 

• • • 

750000 

4 " 

525 

44.8 

80000C 

... 

550 

• « • 

90000C 

) ... 

600 

• • • 

100000 C 

4y 2 " 

650 

55.2 


Calculated Carrying Capacities 72° F. rise 


Cft 


Short time in minutes 


24 

30 

38 

60 

70 

80 

90 

110 

125 

135 

140 

185 

215 

240 

250 

280 

335 

375 

415 

480 

545 

600 

630 

660 

700 

740 


30 


26 

33 

43 

60 

86 

95 

110 

130 

150 

175 

205 

245 

300 

350 

360 

420 

485 

560 

630 

750 

860 

950 

1020 

1050 

1140 

1215 



15 

10 

5 


31 

34 

42 


37 

41 

50 


50 

55 

65 


70 

85 

95 


105 

115 

150 


125 

140 

180 


140 

155 

200 


150 

190 

235 


175 

220 

275 


215 

250 

316 


255 

290 

385 


310 

360 

440 


380 

430 

565 


430 

520 

675 


455 

550 

720 


525 

640 

820 


610 

750 

965 


700 

845 

1105 


775 

965 

1190 


925 

1130 

1520 


1050 

1280 

1700 


1160 

1435 

1960 


1220 

1510 

2030 


1260 

1560 

2135 


1365 

1690 

2330 


1460 

1840 

2520 




















































338 


ELECTRICAL TABLES AND DATA 


Table CXXXIV 
Open Wires 

Table of Carrying Capacities; open wires. 

20° C.; 36° F. temperature rise above surrounding air. 
Use this table for rubber covered wires where tempera¬ 
ture does not exceed 85° F., and for “Other insulations" 
where temperature is between 85° F. and 125° F. 



N. E. 

CODE 

Calculated Carrying Capacities 36 

0 F. riaa 

B & S. 
gauge 

Carrying 

capacity 

amperes 

Est. temp, 
rise 
deg. F. 

Indefinite 

time 

amperes 


Short time 

in minutes 

30 

15 

10 

5 

14 

20 

21.6 

25 

25 

29 

33 

37 

12 

25 

19.1 

31 

31 

39 

42 

47 

10 

30 

18.0 

41 

41 

47 

53 

60 

8 

50 

27.9 

52 

52 

60 

66 

75 

e 

70 

29.5 

67 

67 

80 

87 

95 

5 

80 

• • • 

80 

80 

90 

100 

112 

4 

90 

32.0 

90 

90 

105 

120 

137 

2 

100 

26.1 

100 

100 

125 

145 

168 

2 

125 

30.6 

120 

120 

150 

175 

210 

1 

150 

32.4 

140 

145 

180 

220 

265 

0 

200 

40.0 

160 

165 

215 

260 

330 

2/0 

225 

41.2 

186 

210 

250 

310 

380 

3/0 

275 

45.7 

215 

250 

300 

380 

465 

200000 

300 

• • • 

240 

290 

345 

440 

535 

4/0 

325 

56.0 

250 

300 

360 

450 

560 

250000 

350 

• • • 

285 

335 

410 

520 

660 

300000 

400 

38.0 

325 

400 

475 

620 

765 

350000 

450 

• • • 

360 

450 

545 

700 

895 

400000 

500 

47.0 

400 

500 

600 

790 

1020 

500000 

600 

51.4 

480 

600 

730 

950 

1220 

600000 

680 

• • • 

560 

690 

860 

1110 

1565 

700000 

760 

• • • 

625 

775 

970 

1260 

1785 

750000 

800 

57.0 

650 

800 

1025 

1340 

1910 

800000 

840 

• • • 

680 

850 

1090 

1400 

2040 

900000 

920 

• • • 

730 

930 

1190 

1550 

2300 

1000000 

1000 

54.0 

775 

1000 

1285 

1665 

2500 
























ELECTRICAL TABLES AND DATA 


33* 


Table CXXXV 
Open Wires 

Table of Carrying Capacities; open wires. 

40° C.; 72° F. temperature rise above surrounding air. 
Use this table for “Other insulations” where temperature 
floes not exceed 80° F„ and tor rubber covered wires where 
temperature does not exceed 50° F. 


B & S. 
gauge 


N. E. CODE 


14 

12 

10 

8 

6 

5 

4 

3 

2 

1 

0 

2/0 

3/0 

200000 

4/0 

250000 

300000 

350000 

400000 

500000 

600000 

700000 

750000 

800000 

900000 

1000000 


Calculated Carrying Capacities 72° P. rise 


Carrying 

capacity 

amperes 

Est. temp, 
rise 
deg. F. 

Indefinite 

time 

amperes 

abort time 

in minutes 


30 

15 

10 

5 

20 

21.6 

34 

34 

40 

46 

52 

25 

19.1 

43 

43 

54 

59 

65 

30 

18.0 

57 

57 

67 

74 

83 

50 

27.9 

72 

72 

84 

92 

103 

70 

29.5 

94 

94 

109 

122 

134 

80 


110 

110 

127 

141 

157 

90 

32.0 

125 

125 

145 

165 

190 

100 

26.1 

145 

145 

175 

202 

234 

125 

30.6 

168 

170 

205 

245 

295 

150 

32.4 

195 

205 

250 

309 

372 

200 

40.0 

225 

235 

300 

360 

460 

225 

41.2 

260 

290 

350 

430 

530 

275 

45.7 

300 

345 

410 

520 

645 

300 


335 

400 

480 

610 

750 

325 

56.0 

350 

410 

500 

630 

785 

350 


400 

470 

575 

730 

925 

400 

38.0 

450 

550 

660 

860 

1070 

450 


500 

630 

760 

980 

1250 

500 

47\0 

560 

700 

840 

1100 

1425 

600 

51.4 

670 

840 

1025 

1330 

1785 

680 


780 

965 

1200 

1550 

2190 

760 


870 

1080 

1370 

1760 

2500 

800 

57To 

910 

1110 

1435 

1860 

2675 

840 


95C 

1190 

1525 

1960 

2855 

920 


1020 

1300 

1665 

2150 

3215 

1000 

510 

1085 

1400 

1800 

2330 

3500 
















































340 ELECTRICAL. TABLES AND DATA 

Table CXXXVI 
Wires in Conduit 

Limiting 


Outer 

Temper¬ 







Temp. 

ature 







■Oth¬ 

Rub¬ 

Range in 

3 No. 14 Wires in %" Conduit 

Cooling Load; 

er 

ber 

Conduit 


Heating load; 

amperes 

Amperes 

Ins. 

Ins. 

F. 

15 

20 

25 

45 

7% 

0 

123 

93 

22-27 

2280 

250 

110 

15 

300 

180 

118 

88 

27-32 


300 

120 

15 

210 

130 

113 

83 

32-37 


450 

160 

15 

195 

100 

108 

78 

37-42 


660 

180 

15 

125 

80 

103 

73 

42-47 


1560 

210 

15 

95 

70 

98 

68 

47-52 



220 

15 

80 

60 

93 

63 

52-57 



350 

15 

60 

60 

88 

58 

57-62 



400 

15 

40 

40 

83 

53 

62-67 



540 

15 

40 

40 

78 

48 

67-72 



1350 

15 

40 

40 

Limiting 








Outer 

Temper¬ 







Temp. 

ature 







Oth¬ 

Rub¬ 

Range in 

3 No. 12 Wires in %" Conduit Cooling Load: 

er 

ber 

Conduit 


Heating load; amperes 

Amperes 

Ins. 

Ins. 

F. 

20 

25 

35 

60 

10 

0 

123 

93 

22-27 

840 

200 

50 

13 

230 

200 

118 

88 

27-32 


270 

50 

13 

200 

150 

113 

83 

32-37 


500 

60 

13 

170 

100 

108 

78 

37-42 


660 

80 

13 

120 

100 

103 

73 

42-47 


2000 

100 

13 

100 

100 

98 

68 

47-52 



100 

13 

100 

90 

93 

63 

52-57 



120 

13 

80 

80 

88 

58 

57-62 



200 

13 

50 

50 

83 

53 

62-67 



200 

13 

50 

50 

78 

48 

67-72 



220 

13 

50 

50 

Limiting 








Outer 

Temper¬ 







Temp. 

ature 







Oth¬ 

Rub¬ 

Range in 

3 No. 10 Wires in %" Conduit 

Cooling Load; 

er 

ber 

Conduit 


Heating load; amperes 

Amperes 

Ins. 

Ins. 

F. 

25 

35 

50 

75 

12% 

0 

123 

93 

22-27 

1380 

210 

60 

21 

360 

270 

118 

88 

27-32 


210 

60 

21 

250 

225 

113 

83 

32-37 


270 

65 

21 

200 

150 

108 

78 

37-42 


300 

70 

21 

150 

130 

103 

73 

42-47 


540 

75 

21 

90 

115 

98 

68 

47-52 


1440 

80 

21 

90 

85 

93 

63 

52-57 



90 

21 

90 

75 

88 

58 

57-62 



120 

21 

90 

75 

83 

53 

62-57 



140 

21 

90 

75 

83 

53 

62-67 



140 

21 

90 

75 

78 

48 

67-72 



160 

21 

90 

75 


ELECTRICAL TABLES AND DATA. 
Table CXXXYII 
Wibes in Conduit 


341 


Limitimg 

Outer Temper- 

Temp. ature 

Oth- Rub- Range in 


er 

ber 

Conduit 

Ins. 

Ins. 

F. 

123 

93 

22-27 

118 

88 

27-32 

113 

83 

32-37 

108 

78 

37-42 

103 

73 

42-47 

98 

68 

47-52 

93 

63 

52-57 

88 

58 

57-62 

83 

53 

62-67 

78 

48 

67-72 

Limiting 


Outer 

Temper¬ 

Temp. 

ature 

Oth¬ 

Rub¬ 

Range in 

er 

ber 

Conduit 

Ins. 

Ins. 

F. 

123 

93 

22-27 

118 

88 

27-32 

113 

83 

32-37 

108 

78 

37-42 

103 

73 

42-47 

98 

68 

47-52 

93 

63 

52-57 

88 

58 

57-62 

83 

53 

62-67 

78 

48 

67-72 

Limiting 


Outer 

Temper¬ 

Temp. 

ature 

Oth¬ 

Rub¬ 

Range in 

er 

ber 

Conduit 

Ins. 

Ins. 

F. 

123 

93 

22-27 

118 

88 

27-32 

113 

83 

32-37 

108 

78 

37-42 

103 

73 

42-47 

98 

68 

47-52 

93 

63 

52-57 

88 

58 

57-62 

83 

53 

62-67 

78 

48 

67-72 


3 No. 8 Wires in Conduit Cooling Load; 



Heating load; amperes 

Amperes 

35 

50 

70 

105 

17 % 

u 

1380 

210 

60 

21 

510 

420 


240 

60 

21 

345 

290 


270 

70 

21 

285 

210 


350 

80 

21 

240 

160 


540 

90 

21 

180 

120 


900 

100 

21 

120 

100 


1360 

105 

21 

100 

100 



110 

21 

90 

90 



115 

21 

90 

90 



120 

21 

90 

90 


3 No. 6 

Wires in Conduit 

Cooling Load; 

Heating load: amperes 

Amperes 

50 70 

80 

100 

150 

3b 

w 

1000 120 

100 

45 

19 

600 

330 

1920 180 

100 

50 

19 

420 

240 

200 

100 

60 

19 

300 

225 

220 

120 

80 

19 

220 

200 

300 

140 

80 

19 

180 

120 

360 

160 

90 

19 

120 

100 

450 

180 

90 

19 

100 

100 

630 

220 

90 

19 

100 

100 

840 

240 

90 

19 

100 

100 

1260 

260 

10 

19 

100 

100 


3 No. 4 

Wires in Conduit 

Cooling Load; 


Heating load; amperes 


Amperes 

70 

80 

90 

100 

140 210 

3b 

e 

600 

360 

240 

135 

50 

22 

720 

300 

900 

450 

270 

150 

50 

22 

480 

270 

1260 

510 

300 

160 

60 

22 

480 

210 

2400 

630 

390 

200 

70 

22 

320 

150 


1080 

480 

240 

70 

22 

220 

120 



600 

360 

70 

22 

180 

110 



950 

450 

75 

22 

150 

90 



1800 

510 

75 

22 

130 

80 




570 

75 

22 

130 

60 




780 

80 

22 

130 

60 


342 


ELECTRICAL. TABLES AND DATA 


Table CXXXVIII 
Wires in Conduit 

Limiting 


Outer 

Temper¬ 








Temp. 

Of h- Rub- 

ature 
Range in 

3 No. 3 Wires in 1 % " Conduit 

Cooling Load; 

er 

her 

Conduit 

Heating load; amperes 

Amperes 

Ins 

Ins. 

F. 

80 

90 

100 

160 

240 

40 

u 

123 

93 

22-27 

780 

480 

240 

60 

28 

600 

420 

118 

88 

27-32 

1500 

645 

300 

60 

28 

400 

300 

113 

83 

32-37 


900 

400 

70 

28 

330 

175 

108 

78 

37-42 


1300 

570 

72 

28 

300 

100 

103 

73 

42-47 



780 

74 

28 

250 

100 

98 

68 

47-52 




76 

28 

240 

100 

93 

63 

52-57 




80 

28 

200 

75 

88 

58 

57-62 




85 

28 

150 

75 

83 

53 

62-67 




85 

28 

150 

75 

78 

48 

67-72 




85 

28 

150 

75 

Limiting 









Outer 

Temper¬ 








Temn. 

ature 








Oth¬ 

Rub¬ 

Range in 

3 No. 2 Wires in iy 2 " Conduit 

Cooling Load; 

er 

ber 

Conduit 

Heating load; amperes 

Amperes 

Ins. 

Ins. 

F. 

90 

125 

180 

270 


45 

0 

123 

93 

22-27 

840 

240 

65 

25 


660 

480 

118 

88 

27-32 

1560 

260 

70 

25 


450 

350 

113 

83 

32-37 


320 

75 

25 


345 

240 

108 

78 

37-42 


360 

85 

25 


270 

200 

103 

73 

42-47 


570 

95 

25 


165 

150 

98 

68 

47-52 


720 

95 

25 


155 

110 

93 

63 

52-57 


1000 

95 

25 


155 

no 

88 

58 

57-62 


1900 

95 

25 


155 

no 

83 

53 

62-67 



100 

25 


155 

no 

78 

48 

67-72 



100 

25 


155 

100 

Limiting 









Outer 

Temper¬ 








Temp. 

ature 








Oth¬ 

Rub¬ 

Range in 

3 No. 1 Wires in IVz" Conduit 

Cooling Load; 

er 

ber 

Conduit 


Heating load; amperes 

Amperes 

Ins. 

Ins. 

F. 

100 

125 

150 

200 

300 

50 

0 

123 

93 

22-27 

840 

310 

170 

90 

29 

750 

480 

118 

88 

27-32 

1020 

330 

‘180 

90 

29 

580 

360 

113 

83 

32-37 

1560 

420 

200 

100 

29 

420 

300 

108 

78 

37-42 


600 

220 

100 

29 

360 

270 

103 

73 

42-47 


810 

240 

110 

29 

270 

195 

98 

68 

47-52 


1000 

270 

110 

29 

220 

165 

93 

63 

52-57 


1560 

390 

125 

29 

180 

135 

88 

58 

57-62 



450 

135 

29 

150 

135 

83 

53 

62-67 



480 

135 

29 

150 

135 

78 

48 

67-72 



720 

140 

29 

150 

135 


ELECTRICAL, TABLES AND DATA 


343 


Limiting 

Outer Temper- 

Temp. ature 

Oth- Rub- 


Table CXXXIX 
Wires in Conduit 

3 No. 0 Wires in Conduit Cooling Load; 


er 

ber 

Conduit 

Heating load; amperes 

Amperes 

Ins. 

Ins. 

F. 

125 

175 

250 

375 

62% 

0 

123 

93 

22-27 

550 

190 

85 

32 

840 

525 

118 

88 

27-32 

800 

210 

85 

32 

600 

390 

113 

83 

32-37 

1140 

230 

85 

32 

480 

300 

108 

78 

37-42 

2000 

250 

85 

32 

420 

225 

103 

73 

42-47 


300 

85 

32 

350 

200 

98 

68 

47-52 


400 

95 

32 

300 

190 

93 

63 

52-57 


480 

115 

32 

270 

180 

88 

58 

57-62 


540 

135 

32 

190 

140 

83 

53 

62-67 


700 

135 

32 

190 

140 

78 

48 

67-72 


1140 

135 

32 

190 

140 

Limiting 








Outer 

Temper¬ 







TemD. 

ature 







Oth¬ 

Rub¬ 

Range in 

3 

No.00 

Wires in Conduit 

Cooling Load; 

er 

ber 

Conduit 

Heating load; 

amperes 

Amperes 

Ins. 

Ins. 

F. 

150 

225 

300 

450 

75 

0 

123 

93 

22-27 

700 

180 

60 

31 

900 

500 

118 

88 

27-32 

960 

190 

60 

31 

720 

360 

113 

83 

32-37 

1680 

210 

60 

31 

570 

330 

108 

78 

37-42 

4000 

220 

90 

31 

435 

315 

103 

73 

42-47 


230 

90 

31 

360 

240 

98 

68 

47-52 


250 

90 

31 

250 

210 

93 

63 

52-57 


265 

105 

31 

195 

160 

88 

58 

57-62 


285 

105 

31 

160 

130 

83 

53 

62-67 


315 

105 

31 

160 

130 

78 

48 

67-72 


400 

105 

31 

160 

130 

Limiting 








Outer 

Temper¬ 







TemD. 

ature 







Oth¬ 

Rub¬ 

Range in 

3 No. 000 Wires in Conduit 

Cooling Load: 

er 

ber 

Conduit 


Heating load; amperes 

Amperes 

Ins. 

Ins. 

F. 

175 

262% 

350 

525 

87% 

0 

123 

93 

22-27 

1100 

200 

100 

38 

960 

540 

118 

88 

27-32 

1470 

210 

100 

38 

660 

480 

113 

83 

32-37 

2300 

220 

100 

38 

560 

450 

108 

78 

37-42 


240 

110 

38 

500 

350 

103 

73 

42-47 


270 

110 

38 

480 

310 

98 

68 

47-52 


300 

no 

38 

360 

270 

93 

63 

52-57 


360 

120 

38 

315 

180 

88 

58 

57-62 


420 

135 

38 

210 

120 

83 

53 

62-67 


480 

135 

38 

180 

120 

78 

48 

67-72 


660 

135 

38 

180 

120 


344 


ELECTRICAL TABLElS AND DATA’ 
Table CXL 


Wires in Conduit 


Limiting 
Outer 
Temp. 
Oth- Rub¬ 
er ber 

Ins. Ins. 

123 93 

Temper¬ 
ature 
Range in 
Conduit 
F. 

22-27 

3 No. 200,000 C. M. Cables 
estimated 

Heating load; amperes 

212 265 318 380 424 636 

420 180 135 100 72 29 

Cooling Load; 
Amperes 
106 0 
2040 660 

118 

88 

27-32 

495 

220 

135 

100 

72 29 

1320 

540 

113 

83 

32-37 

600 

240 

140 

100 

72 29 

780 

450 

108 

78 

37-42 

780 

250 

140 

100 

72 29 

570 

300 

103 

73 

42-47 

1200 

270 

150 

100 

72 29 

450 

300 

98 

68 

47-52 

1980 

300 

150 

100 

72 29 

390 

240 

93 

63 

52-57 

3300 

340 

165 

100 

72 29 

270 

180 

88 

58 

57-62 


380 

165 

100 

72 29 

170 

150 

83 

53 

62-67 


400 

240 

100 

72 29 

170 

150 

78 

48 

67-72 


480 

240 

100 

72 29 

170 

150 

Limiting 
Outer 
Temp. 
Oth-Rub¬ 
er ber 

Ins. Ins. 

123 

Temper¬ 
ature 
Range in 
Conduit 

F. 

22-27 

3 No.400 Cables in 2V 2 ” Conduit Cooling Load; 

Heating load; amperes Amperes 

225 281 337 393 450 675 112*4 0 

420 180 135 100 72 29 2040 660 

118 


27-32 

495 

220 

135 

100 

72 29 

1320 

540 

113 


32-37 

600 

240 

140 

100 

72 29 

780 

450 

108 


37-42 

780 

250 

140 

100 

72 29 

570 

300 

103 


42-47 

1200 

270 

150 

100 

72 29 

450 

300 

98 


47-52 

1980 

300 

150 

100 

72 29 

390 

240 

93 


52-57 

3300 

340 

165 

100 

72 29 

270 

180 

88 


57-62 


380 

165 

100 

72 29 

170 

150 

83 


62-67 


400 

240 

100 

72 29 

170 

150 

78 


67-72 


480 

240 

100 

72 29 

170 

150 

Limiting 
Outer 
Temp. 
Oth- Rub¬ 
er ber 

Ins. Ins. 
123 93 

Temper¬ 
ature 
Range in 
Conduit 

F. 

22-27 

3 No. 250,000 C. M. Cables 
estimated 

Heating load; amperes 

250 312 375 437 500 750 

420 180 135 100 72 29 

Cooling Load; 
Amperes 

125 0 

2040 660 

118 

88 

27-32 

495 

220 

135 

100 

72 29 

1320 

540 

113 

83 

32-37 

600 

240 

140 

100 

72 29 

780 

450 

108 

78 

37-42 

780 

250 

140 

100 

72 29 

570 

360 

103 

73 

42-47 

1200 

270 

150 

100 

72 29 

450 

300 

98 

68 

47-52 

1980 

300 

150 

100 

72 29 

390 

240 

93 

63 

52-57 

3300 

340 

165 

100 

72 29 

270 

180 

88 

58 

57-62 


380 

165 

100 

72 29 

170 

150 

83 

53 

62-67 


400 

240 

100 

72 29 

170 

150 

78 

48 

67-72 


480 

240 

100 

72 29 

170 

150 


ELECTRICAL TABLES AND DATA 

Table CXLI 

Wires in Conduit 


345 


Limiting 


Outer 

Temr>. 

Temper¬ 

ature 

3 No. 300,000 C. 

M. Cables 

Oth¬ 

Rub¬ 

Range in 


in 3" Conduit 


er 

ber 

Conduit 

Heating load; amperes 

Ins. 

Ins. 

F. 

275 

343 

412 

550 

825 

123 

93 

22-27 

720 

360 

120 

100 

33 

118 

88 

27-32 

840 

370 

150 

100 

33 

113 

83 

32-37 

1320 

400 

160 

100 

33 

108 

78 

37-42 

1980 

420 

170 

100 

33 

103 

73 

42-47 


450 

180 

100 

33 

98 

68 

47-52 


540 

190 

100 

33 

93 

63 

52-57 


810 

250 

100 

33 

88 

58 

57-62 


1080 

300 

100 

33 

83 

53 

62-67 


2040 

350 

100 

33 

78 

48 

67-72 



400 

100 

33 

Limiting 

Temper¬ 

ature 






Outer 

Tpm n 

3 No. 350,000 C. 

M. Cables 

Oth¬ 

Rub¬ 

Range in 


in Conduit, estimated 

er 

ber 

Conduit 


Heating load 

; amperes 

Ins. 

Ins. 

F. 

300 

375 

450 

600 

900 

123 

93 

22-27 

840 

370 

165 

105 

40 

118 

88 

27-32 

1000 

400 

185 

105 

40 

113 

83 

32-37 

3000 

455 

200 

105 

40 

108 

78 

37-42 


480 

210 

105 

40 

103 

73 

42-47 


540 

225 

105 

40 

98 

68 

47-52 


630 

240 

105 

40 

93 

63 

52-57 


825 

315 

105 

40 

88 

58 

57-62 


1080 

350 

105 

40 

83 

53 

62-67 


1900 

415 

105 

40 

78 

48 

67-72 



470 

105 

40 

Limiting 







Outer 

Temn. 

Temper¬ 

ature 

3 No. 400,000 C. M. Cables 

Oth¬ 

Rub¬ 

Range in 


in 3 Conduit 


er 

ber 

Conduit 


Heating load; amperes 

Ins 

Ins. 

F 

325 

406 

487 

650 

975 

123 

93 

22-27 

960 

390 

210 

no 

46 

118 

88 

27-32 

1170 

430 

225 

no 

46 

113 

83 

32-37 

1800 

510 

235 

no 

46 

108 

78 

37-42 

4000 

540 

250 

no 

46 

103 

73 

42-47 


630 

265 

no 

46 

98 

68 

47-52 


720 

290 

no 

46 

93 

63 

52-57 


840 

330 

no 

46 

88 

58 

57-62 


1080 

400 

no 

46 

83 

53 

62-67 


1740 

480 

no 

46 

78 

48 

67-72 


4000 

540 

no 

46 


Cooling Load; . 
Amperes 

137 0 

1140 480 

690 400 

600 360 

480 260 
360 240 

300 220 

280 180 
210 150 

210 150 

210 150 


Cooling Load; 
Amperes 


150 

0 

1070 

600 

780 

485 

660 

435 

600 

370 

480‘ 

320 

400 

260 

315 

210 

300 

200 

250 

175 

220 

165 


Cooling Load; 
Amperes 

162 y 2 0 

990 720 

870 570 

720 510 

615 480 

600 400 
510 300 

480 270 

330 250 

300 200 
240 180 




346 ELECTRICAL TABLES AND DATA 

Table CXLII 
Wires in Conduit 

Limiting 1 


Outer 
Temp. 
Oth- Rub¬ 
er ber 
Ins. Ins. 
123 93 

Tempei- 
ature 
Range in 
Conduit 
F. 

22-27 

3 

400 

1050 

No. 500,000 C. M. Cables 

in 3" Conduit Cooling Load; 

Heating load; amperes Amperes 

500 600 700 800 1200 200 0 

360 250 165 122 42 3500 1080 

118 

88 

27-32 

1140 

400 

270 

165 

122 

42 

1620 

950 

113 

83 

32-37 

1440 

430 

300 

175 

122 

42 

1200 

720 

108 

78 

37-42 

1860 

480 

330 

175 

122 

42 

900 

540 

103 

73 

42-47 

2700 

560 

360 

195 

122 

42 

870 

450 

98 

68 

47-52 


650 

390 

195 

122 

42 

600 

360 

93 

63 

52-57 


750 

420 

210 

122 

42 

500 

300 

88 

58 

57-62 


870 

450 

210 

122 

42 

440 

240 

83 

53 

62-67 


960 

465 

225 

122 

42 

280 

160 

78 

48 

67-72 


1260 

480 

225 

122 42 

200 

110 

Limiting 
Outer 
Temp. 
Oth- Rub¬ 
er ber 
Ins. Ins. 
123 93 

Temper¬ 
ature 
Range in 
Conduit 
F. 

22-27 

3 

450 

1000 

No. 600,000 C. M. Cables 
in Conduit, estimated Cooling Load; 

Heating load; amperes Amperes 

562 675 785 900 1350 230 0 

420 240 160 122 42 2280 900 

118 

88 

27-32 

1110 

450 

250 

160 

122 

42 

1500 

720 

113 

83 

32-37 

1440 

480 

260 

160 

122 

42 

1150 

600 

108 

78 

37-42 

2340 

580 

270 

160 

122 

42 

900 

500 

103 

73 

42-47 

3500 

660 

290 

160 

122 

42 

750 

480 

98 

68 

47-52 


720 

320 

160 

122 

42 

660 

420 

93 

63 

52-57 


780 

360 

160 

122 

42 

600 

390 

88 

58 

57-62 


1020 

410 

160 

122 

42 

510 

360 

83 

53 

62-67 


1500 

420 

160 

122 

42 

420 

300 

78 

48 

67-72 



430 

160 

122 

42 

270 

250 

Limiting 
Outer 
Temp. 
Oth- Rub¬ 
er ber 

Ins. Ins. 

123 93 

Temper¬ 
ature 
Range in 
Conduit 
F. 

22-27 

3 

505 

1000 

No. 700,000 C. M. Cables 
in Conduit, estimated Cooling Load; 

Heating load; amperes Amperes 

630 757 880 1010 1515 253 0 

420 240 160 130 45 2280 900 

118 

88 

27-32 

1110 

450 

250 

160 

130 

45 

1500 

720 

113 

83 

32-37 

1440 

480 

260 

160 

130 

45 

1150 

600 

108 

78 

37-42 

2340 

600 

270 

160 

130 

45 

900 

500 

103 

73 

42-47 

3500 

660 

300 

160 

130 

45 

750 

480 

98 

68 

47-52 


720 

340 

160 

130 

45 

660 

420 

93 

63 

52-57 


780 

380 

160 

130 

45 

600 

390 

88 

58 

57-62 


1020 

420 

160 

130 

45 

510 

360 

83 

53 

62-67 


1500 

460 

160 

130 

45 

420 

300 

78 

48 

67-72 



500 

160 

130 

45 

270 

250 


ELECTRICAL TABLES AND DATA 347 

Table CXLIIJ 


Wires in Conduit 


Limiting 









Outer 

Temper¬ 








Tpmn. 

ature 

3 No. 750,000 C. M. Cables 



Oth¬ 

Rub¬ 

Range in 


in 4" Conduit 


Cooling Load; 

er 

ber 

Conduit 

Heating load; 

amperes 

Amperes 

Ins. 

Ins. 

F. 

525 

656 

787 

1050 1575 

262% 

0 

123 

93 

22-27 

900 

420 

230 

150 

54 

2280 

900 

118 

88 

27-32 

1110 

450 

240 

150 

54 

1500 

720 

113 

83 

32-37 

1440 

480 

250 

150 

54 

1150 

600 

108 

78 

37-42 

2340 

570 

270 

150 

54 

900 

500 

103 

73 

42-47 

3500 

660 

300 

150 

54 

750 

460 

98 

68 

47-52 


720 

340 

150 

54 

660 

420 

93 

63 

52-57 


780 

370 

150 

54 

600 

390 

88 

58 

57-62 


1020 

410 

150 

54 

510 

360 

83 

53 

62-67 


1500 

450 

150 

54 

420 

300 

78 

48 

67-72 



500 

150 

54 

270 

250 

Limiting 









Outer 

T'pm r> 

Temper¬ 

ature 

3 No. 800,000 C. M. Cables 



Oth¬ 

Rub¬ 

Range in 


in Conduit, estimated 

Cooling‘ Load , 

er 

ber 

Conduit 

Heating load; 

; amperes 

Amperes 

Ins 

Ins. 

F. 

550 

688 

825 

1100 1650 

275 

0 

123 

93 

22-27 

900 

420 

230 

150 

54 

2280 

900 

118 

88 

27-32 

1110 

450 

240 

150 

54 

1500 

720 

113 

83 

32-37 

1440 

480 

250 

150 

54 

1150 

600 

108 

78 

37-42 

2340 

570 

270 

150 

54 

900 

500 

103 

73 

42-47 

3500 

660 

300 

150 

54 

750 

460 

98 

68 

47-52 


720 

340 

150 

54 

660 

420 

93 

63 

52-57 


780 

370 

150 

54 

600 

390 

88 

58 

57-62 


1020 

410 

150 

54 

510 

360 

83 

53 

62-67 


1500 

450 

150 

54 

420 

300 

78 

48 

67-72 



500 

150 

54 

270 

250 

Limiting 









Outer 

Tpm d 

Temper¬ 

ature 

3 No. 900,000 C. M. Cables 



X cm t-'• 

Oth- 'Rub- 

Range in 


in Conduit, estimated 

Cooling Load; 

er 

ber 

Conduit 


Heating load 

; amperes 

Amperes 

Ins 

Ins. 

F. 

600 

750 

900 

1200 1800 

3UU 


123 

93 

22-27 

920 

420 

250 

100 

50 

2500 

930 

118 

88 

27-32 

1020 

465 

260 

100 

50 

1560 

780 

113 

83 

32-37 

1200 

480 

270 

100 

50 

1320 

720 

108 

78 

37-42 

1350 

500 

280 

100 

50 

1050 

660 

103 

73 

42-47 

2250 

530 

290 

100 

50 

870 

600 

98 

68 

47-52 


550 

300 

100 

50 

780 

540 

93 

63 

52-57 


600 

330 

100 

50 

670 

485 

88 

58 

57-62 


690 

345 

100 

50 

600 

450 

83 

53 

62-67 


960 

370 

100 

50 

400 

360 

78 

48 

67-72 


1400 

450 

100 

50 

330 

300 





348 


ELECTRICAL TABLES AND DATA 


Table CXLIV 


Wires in Conduit 


Limiting 
Outer 
Temp. 
Oth- Rub' 
er ber 


Temper¬ 
ature 
Range in 
Conduit 


3 No. 1,000,000 C. M. Cables 
in 4 % " Conduit 
Heating load; amperes 


Cooling Load; 
Amperes 


Ins. 

Ins. 

F. 

650 

812 

975 

1300 1950 

325 

0 

123 

93 

22-27 

930 

420 

250 

100 

50 

2500 

930 

118 

88 

27-32 

1020 

465 

260 

100 

50 

1560 

780 

113 

83 

32-37 

1200 

480 

270 

100 

50 

1320 

720 

108 

78 

37-42 

1350 

500 

280 

100 

50 

1050 

660 

103 

73 

42-47 

2250 

530 

290 

100 

50 

870 

600 

98 

68 

47-52 


550 

300 

100 

50 

780 

540 

93 

63 

52-57 


600 

330 

100 

50 

670 

485 

88 

58 

57-62 


690 

345 

100 

50 

600 

450 

83 

53 

62-67 


960 

385 

100 

50 

400 

36C 

78 

48 

67-72 


1400 

450 

100 

50 

330 

300 


ELECTRICAL TABLES AND DATA 349 

Table CXLV 
Open Wires 


Limiting 

Outer Temper- 

Temp. , ature 


Oth¬ 

Rub¬ 

Range of 

No. 14 D. B. R. C. 

Wire in Air 

Cooling Load; 

er 

ber 

Wire 

Heating load 

; amperes 

Amperes 

Ins. 

Ins. 

F. 

15 20 25 

45 

0 

123 

93 

22-27 

120 

21 

21 

118 

88 

27-32 

390 

21 

21 

113 

83 

32-37 


21 

21 

108 

78 

37-42 


21 

21 

103 

73 

42-47 


21 

21 

98 

68 

47-52 


21 

21 

93 

63 

52-57 


21 

21 

88 

58 

57-62 


21 

21 

83 

53 

62-67 


21 

21 

78 

48 

67-72 


21 



Limiting 
Outer 
Temp. 
Oth- Rub- 

Temper¬ 
ature 
Range of 

* 

No. 12 D. B. R. C. Wire in Air 

Cooling Load; 

er 

ber 

Wire 

Heating load; amperes 

Amperes 

Ins. 

Ins. 

F. 

20 25 36 60 

0 

123 

93 

22-27 

120 21 

24 

118 

88 

27-32 

150 21 

24 

113 

83 

32-37 

660 21 

24 

108 

78 

37-42 

21 

24 

103 

73 

42-47 

21 

24 

98 

68 

47-52 

21 

24 

93 

63 

52-57 

21 

24 

88 

58 

57-62 

21 

24 

83 

53 

62-67 

21 

24 

78 

48 

67-72 

21 

24 


Limiting 
Outer 
Temp. 
Oth- Rub¬ 

Temper¬ 
ature 
Range of 

No. 10 D. B. R. C. 

Wire in Air 

Cooling Load; 

er ber 

Wire 

Heating load; amperes 

Amperes • 

Ins. Ins. 

F 

25 35 50 

75 

0 

123 

93 

22-27 

1020 80 

32 

21 

118 

88 

27-32 

90 

32 

21 

113 

83 

32-37 

180 

32 

21 

108 

78 

37-42 

300 

32 

21 

103 

73 

42-47 

• 

32 

21 

98 

68 

47-52 


32 

21 

93 

63 

52-57 


32 

21 

88 

58 

57-62 


32 

21 

83 

53 

62-67 


32 

21 

78 

48 

67-72 


32 

21 


350 ELECTRICAL TABLES AND DATA 

Table CXLVI 
Open Wires 

Limiting 

Outer 


Temp. 
Oth- Rub¬ 

Temper¬ 

ature 

No. 8 D. B. R. C. Wire in Air 

Cooling Load; 

er ber 

Range 

Heating load; amperes 

Amperes 

Ins. Ins. 

F. 

35 50 70 105 

0 

123 

93 

22-27 

960 60 23 

40 

118 

88 

27-32 

70 23 

40 

113 

83 

32-37 

85 23 

40 

108 

78 

37-42 

100 23 

40 

103 

73 

42-47 

180 23 

40 

98 

68 

47-52 

1350 23 

40 

93 

63 

52-57 

23 

40 

88 

58 

57-62 

23 

40 

83 

53 

62-67 

23 

40 

78 

48 

67-72 

23 

40 

Limiting 
Outer 
Temp. 
Oth- Rub¬ 

Temper¬ 

ature 

No. 6 D. B. R. C. Wire in Air 

Cooling Load; 

er ber 

Range 

Heating load; amperes 

Amperes 

Ins. Ins. 

F. 

50 70 80 100 

0 

123 

93 

22-27 

420 150 21 

80 

118 

88 

27-32 

240 21 

70 

113 

83 

32-37 

650 21 

60 

108 

78 

37-42 

21 

50 

103 

73 

42-47 

21 

40 

98 

68 

47-52 

21 

30 

93 

63 

52-57 

21 

30 

88 

58 

57-62 

21 

30 

83 

53 

62-67 

21 

30 

78 

48 

67-72 

21 

30 

Limiting 
Outer 
Temp. 
Oth- Rub¬ 

Temper¬ 

ature 

No. 4 D. B. R. C. Wire in Air 

Cooling Load; 

er ber 

Range 

Heating load; amperes 

Amperes 

Ins. Ins. 

F. 

70 80 90 100 140 210 

0 

123 

93 

22-27 

420 200 60 17 

85 

118 

88 

27-32 

2000 250 66 17 

80 

113 

83 

32-37 

600 60 17 

75 

108 

78 

37-42 

70 17 

70 

103 

73 

42-47 

80 17 

60 

98 

68 

47-52 

90 17 

50 

93 

63 

52-57 

120 17 

40 

88 

58 

57-62 

160 17 

40 

83 

53 

62-67 

240 17 

40 

78 

48 

67-72 

500 17 

40 



ELECTRICAL TABLES AND DATA 


351 


Table CXLVII 


Open Wires 


Limiting 
Outer 
Temp. 
Oth- Rub¬ 
er ber 
Ins. Ins. 

123 93 

Temper¬ 
ature 
Range of 
Wire 

F. 

22-27 

No. 3 D. B. R. C. Wire in Air 
Heating load; amperes 

80 90 100 160 240 

1800 70 27 

Cooling Load; 
Amperes 

0 

90 

118 

88 

27-32 

75 

27 

80 

113 

83 

32-37 

80 

27 

70 

108 

78 

37-42 

85 

27 

60 

103 

73 

42-47 

95 

27 

50 

98 

68 

47-52 

120 

27 

40 

93 

63 

52-57 

180 

27 

40 

88 

58 

57-62 

300 

27 

40 

83 

53 

62-67 

2000 

27 

40 

78 

48 

67-72 


27 

40 


Limiting: 

Outer Temper- 

Temp. ature 


Oth¬ 

er 

Ins. 

123 

Rub¬ 

ber 

Ins. 

93 

Range of 
Wire 

F. 

22-27 

No. 2 D. B. R. C. Wire in Air 
Heating load; amperes 

90 125 180 270 

780 90 32 

Cooling Load; 
Amperes 

45 0 

130 100 

118 

88 

27-32 

95 

32 

90 

80 

113 

83 

32-37 

100 

32 

80 

60 

108 

78 

37-42 

120 

32 

60 

40 

103 

73 

42-47 

200 

32 

52 

40 

98 

68 

47-52 

330 

32 

52 

40 

93 

63 

52-57 

540 

32 

52 

40 

88 

58 

57-62 


32 

52 

40 

83 

53 

62-67 


32 

52 

40 

78 

48 

67-72 


32 

52 

40 


Limiting 
Outer 
Temp. 
Oth- Rub¬ 
er ber 
Ins. Ins. 

123 93 

Temper¬ 
ature 
Range of 
Wire 

F. 

22-27 

No. 1 D. B. R. C. Wire in Air 
Heating load; amperes 

100 125 150 200 300 

540 120 41 

Cooling Load; 
Amperes 

50 0 

150 100 

118 

88 

27-32 

1300 150 

41 

100 

70 

113 

83 

32-37 

200 

41 

60 

60 

108 

78 

37-42 

250 

41 

60 

60 

103 

73 

42-47 

350 

41 

60 

60 

98 

68 

47-52 

500 

41 

60 

60 

93 

63 

52-57 

800 

41 

60 

60 

88 

58 

57-62 


41 

60 

60 

83 

53 

62-67 


41 

60 

60 

78 

48 

67-72 


41 

60 

60 



352 


ELECTRICAL TABLES AND DATA 


Table CXLVII1 
Open Wires 

Limiting 


Outer 
Temp. 
Oth- Rub¬ 
er ber 
Ins. Ins. 

123 93 

Temper¬ 
ature 
Range of 
Wire 

F. 

22-27 

No. 0 D. B. R. C. Cable in Air 
Heating load; amperes 

125 175 250 375 

2000 100 29 

Cooling Load; 
Amperes 
62% 0 
190 72 

118 

88 

27-32 


105 

29 

150 

72 

113 

83 

32-37 


110 

29 

110 

72 

108 

78 

37-42 

% 

115 

29 

100 

72 

103 

73 

42-47 


120 

29 

90 

72 

98 

68 

47-52 


180 

29 

80 

72 

93 

63 

52-57 


300 

29 

72 

60 

88 

58 

57-62 


500 

29 

72 

60 

83 

53 

62-67 


2000 

29 

72 

60 

78 

48 

67-72 



29 

72 

60 

Limiting 
Outer 
Temp. 
Oth- Rub¬ 
er ber 
Ins. Ins. 

123 93 

Temper¬ 
ature 
Range of 
Wire 

F. 

22-27 

No. 00 D. B. R. C. Cable in Air 
Heating load; amperes 

150 225 450 675 

375 100 38 

Cooling Load; 
Amperes 

75 0 

250 160 

118 

88 

27-32 

500 

100 

38 

210 

140 

113 

83 

32-37 

750 

100 

38 

190 

120 

108 

78 

37-42 

1620 

120 

38 

120 

110 

103 

73 

42-47 


140 

38 

70 

80 

98 

68 

47-52 


160 

38 

60 

60 

93 

63 

52-57 


180 

38 

60 

60 

88 

58 

57-62 


200 

38 

60 

60 

83 

53 

62-67 


230 

38 

60 

60 

78 

48 

67-72 


260 

38 

60 

60 

Limiting 
Outer 
Temp. 
Oth- Rub¬ 
er ber 
Ins. Ins. 

123 93 

Temptr- 
ature 
Range of 
Wire 

F. 

22-27 

No. 000 D. B. R. C. 

Heating load; 
175 262*6 350 

390 85 

Cable in Air Cooling Load ; 
amperes Amperes 

525 87% 0 

38 120 250 

118 

88 

27-32 

465 

85 

38 

120 

165 

113 

83 

32-37 

690 

85 

38 

120 

130 

108 

78 

37-42 

2000 

100 

38 

100 

120 

103 

73 

42-47 


125 

38 

90 

no 

98 

68 

47-52 


195 

38 

80 

90 

93 

63 

52-57 


300 

38 

80 

80 

88 

58 

57-62 


405 

38 

70 

70 

83 

53 

62-67 


600 

38 

70 

70 

78 

48 

67-72 


930 

38 

70 

70 


ELECTRICAL TABLES AND DATA 


353 


Table CXLIX 


Open Wibes 


Limiting 






Outer 

Temper¬ 





Temp. 

ature 





Oth- Rub¬ 

Range of 

No. 200,000 C. M. Wire in Air 

Cooling Load; 

er ber 

Wire 

Heating load: amperes 

Amperes 

Ins. Ins. 

F. 

210 315 

420 

630 

0 

123 

93 

22-27 

195 

75 

29 

240 

118 

88 

27-32 

195 

75 

29 

200 

113 

83 

32-37 

195 

75 

29 

135 

108 

78 

37-42 

195 

75 

29 

100 

103 

73 

42-47 

240 

90 

29 

80 

98 

68 

47-52 

300 

105 

29 

80 

93 

63 

52-57 

400 

130 

29 

80 

88 

58 

57-62 

540 

170 

29 

80 

83 

53 

62-67 

1200 

200 

29 

80 

78 

48 

67-72 


250 

29 

80 

Limiting 






Outer 

Temper¬ 





Temp. 

ature 





Oth- Rub¬ 

Range of 

No. 0000 C. M. Cable in Air 

Cooling Load; 

er ber 

Wire 

Heating load; amperes 

Amperes 

Ins. Ins. 

F. 

225 337 

450 

675 

0 

123 

93 

22-27 

2000 195 

75 

29 

240 

118 

88 

27-32 

195 

75 

29 

200 

113 

83 

32-37 

195 

75 

29 

135 

108 

78 

37-42 

195 

75 

29 

100 

103 

73 

42-47 

240 

90 

29 

80 

98 

68 

47-52 

300 

105 

29 

80 

93 

63 

52-57 

400 

130 

29 

80 

88 

58 

57-62 

540 

170 

29 

80 

83 

53 

62-67 

1200 

200 

29 

80 

78 

48 

67-72 


250 

29 

80 

Limiting 






Outer 

Temper¬ 




■ 

Temp. 

ature 





Oth- Rub¬ 

Range of 

No. 250,000 C. M. Cable in Air 

Cooling Load; 

er ber 

Wire 

Heating load; amperes 

Amperes 

Ins. Ins. 

F. 

250 375 

500 

750 

0 

123 

93 

22-27 

200 

100 

35 

150 

118 

88 

27-32 

200 

100 

35 

125 

113 

83 

32-37 

220 

100 

35 

110 

108 

78 

37-42 

250 

100 

35 

90 

103 

73 

42-47 

300 

120 

35 

80 

98 

68 

47-52 

400 

135 

35 

70 

93 

63 

52-57 

500 

160 

35 

60 

88 

58 

57-62 

800 

200 

35 

60 

83 

53 

62-67 

1500 

300 

35 

60 

78 

48 

67-72 


400 

35 

60 


354 ELECTRICAL TABLES AND DATA 

Table CL 
Open Wires 

Limiting 


Outer 
Temp. 
Oth- Rub¬ 
er ber 
Ins. Ins. 

123 93 

Temper¬ 
ature 
Range in 
Conduit 
F. 

22-27 

No. 300,000 C. M. Cable in Air 
Heating load; amperes 

275 343 412 550 825 

1020 285 125 42 

Cooling Load; 
Amperes 

137 0 

240 240 

118 

88 

27-32 

4000 480 135 

42 

210 

210 

113 

83 

32-37 

750 150 

42 

150 

150 

108 

78 

37-42 

2300 160 

42 

120 

120 

103 

73 

42-47 

180 

42 

100 

100 

98 

68 

47-52 

250 

42 

90 

90 

93 

63 

52-57 

275 

42 

80 

80 

88 

58 

57-62 

330 

42 

80 

80 

83 

53 

62-67 

375 

42 

80 

80 

78 

48 

67-72 

600 

42 

80 

80 

Limiting 
Outer 
Temp. 
Oth- Rub¬ 
er ber 
Ins. Ins. 

123 93 

Temper¬ 
ature 
Range in 
Conduit 
F. 

22-27 

No. 350,000 C. M. Cable in Air 
Heating load; amperes 

300 375 450 600 900 

960 300 110 46 

Cooling Load; 
Amperes 

150 0 

360 200 

118 

88 

27-32 

3000 450 120 

46 

240 

150 

113 

83 

32-37 

720 130 

46 

180 

80 

108 

78 

37-42 

1200 165 

46 

150 

80 

103 

73 

42-47 

185 

46 

80 

80 

98 

68 

47-52 

240 

46 

80 

80 

93 

63 

52-57 

290 

46 

80 

80 

88 

58 

57-62 

340 

46 

80 

80 

83 

53 

62-67 

420 

46 

80 

80 

78 

48 

67-72 

500 

46 

80 

80 

Limiting 
Outer 
Temp. 
Oth- Rub¬ 
er ber 
Ins. Ins. 

123 93 

Temper¬ 
ature 
Range in 
Conduit 
F. 

22-27 

No. 400,000 C. M. Cable in Air 

Heating load; amperes 

325 406 487 650 975 

960 300 110 46 

Cooling Load; 
Amperes 

162 0 
360 200 

118 

88 

27-32 

3000 450 120 

46 

240 

150 

113 

83 

32-37 

720 130 

46 

180 

80 

108 

78 

37-42 

1200 165 

46 

150 

80 

103 

73 

42-47 

185 

46 

80 

80 

98 

68 

47-52 

240 

46 

80 

80 

93 

63 

52-57 

290 

46 

80 

80 

88 

58 

57-62 

340 

46 

80 

80 

83 

53 

62-67 

420 

46 

80 

80 

78 

48 

67-72 

500 

46 

80 

80 


ELECTRICAL TABLES AND DATA 


355 


Table CLI 


Open Wires 


Limiting 
Outer 
Temp. 
Oth- Rub¬ 
er ber 
Ins. Ins. 

123 93 

Temper¬ 
ature 
Range in 
Conduit 

F. 

22-27 

No. 500,000 C. M. Cable in Air Cooling Load; 

Heating load; amperes Amperes 

400 500 600 700 800 1200 0 

690 345 190 180 50 480 400 

118 

88 

27-32 

1110 

480 

200 

180 

50 

300 

300 

113 

83 

32-37 

4000 

750 

240 

180 

50 

200 

250 

108 

78 

37-42 


900 

270 

180 

50 

125 

200 

103 

73 

42-47 


1500 

300 

180 

50 

84 

150 

98 

68 

47-52 



360 

180 

50 

84 

84 

93 

63 

52-57 



540 

180 

50 

84 

84 

88 

58 

57-62 



750 

180 

50 

84 

84 

83 

53 

62-67 




180 

50 

84 

84 

78 

48 

67-72 




180 

50 

84 

84 

Limiting 
Outer 
Temp. 
Oth- Rub¬ 
er ber 
Ins. Ins. 

123 93 

Temper¬ 
ature 
Range in 
Conduit 

F. 

22-27 

No. 600,000 C. M. Cable in Air Cooling Load; 

Heating load; amperes Amperes 

450 560 675 786 900 1350 225 

700 360 200 185 52 480 400 

118 

88 

27-32 

1200 

500 

210 

185 

52 

300 

300 

113 

83 

32-37 


775 

250 

185 

52 

200 

250 

108 

78 

37-42 


950 

280 

185 

52 

125 

200 

103 

73 

42-47 


1600 

310 

185 

52 

84 

150 

98 

68 

47-52 



370 

185 

52 

84 

84 

93 

63 

52-57 



550 

185 

52 

84 

84 

88 

58 

57-62 



775 

185 

52 

84 

84 

83 

53 

62-67 




185 

52 

84 

84 

78 

48 

67-72 




185 

52 

84 

84 

Limiting 
Outer 
Temp. 
Oth- Rub¬ 
er ber 
Ins. Ins. 

123 93 

Temper¬ 
ature 
Range in 
Conduit 

F. 

22-27 

No. 700,000 C. M. Cables in Air Cooling Load; 

Heating load; amperes Amperes 

500 625 750 1000 1500 262 0 

660 270 150 53 660 400 

118 

88 

27-32 

840 

300 

160 

53 


450 

300 

113 

83 

32-37 

1410 

375 

170 

53 


400 

250 

108 

78 

37-42 


500 

180 

53 


270 

220 

103 

73 

42-47 


625 

195 

53 


220 

200 

98 

68 

47-52 


775 

210 

53 


200 

200 

93 

63 

52-57 


1200 

240 

53 


150 

150 

88 

58 

57-62 



260 

53 


150 

150 

83 

53 

62-67 



280 

53 


150 

150 

78 

48 

67-72 



300 

53 


150 

150 


356 


ELECTRICAL TABLES AND DATA 


Table CLII 
Open Wires 

Limiting 


Outer 

Temper¬ 







Temp. 

ature 







Oth¬ 

• Rub¬ 

Range of 

No. 750,000 C. M. Cable in Air 

Cooling Load; 

er 

ber 

Wire 

Heating load; amperes 

Amperes 

Ins. 

Ins. 

F. 

525 656 

787 

1050 

1575 

262 

0 

123 

93 

22-27 

660 

270 

150 

54 

660 

400 

118 

88 

27-32 

840 

300 

160 

54 

450 

300 

113 

83 

32-37 

1410 

375 

170 

54 

400 

250 

108 

78 

37-42 


500 

180 

54 

270 

220 

103 

73 

42-47 


625 

195 

54 

220 

200 

98 

68 

47-52 


775 

210 

54 

200 

200 

93 

63 

52-57 


1200 

240 

54 

150 

150 

88 

58 

57-62 



260 

54 

150 

150 

83 

53 

62-67 



280 

54 

150 

150 

78 

48 

67-72 



300 

54 

150 

150 

Limiting 








Outer 

Temper¬ 







Temp. 

ature 







Oth¬ 

Rub¬ 

Range of 

No. 800,000 C. M. Cable in Air 

Cooling Load;' 

er 

ber 

Wire 

Heating load: amperes 

Amperes 

Ins. 

Ins. 

F. 

550 687 

825 

1100 

1650 

275 

0 

123 

93 

22-27 

660 

270 

150 

56 

660 

400 

118 

88 

27-32 

840 

300 

160 

56 

450 

300 

113 

83 

32-37 

1410 

275 

170 

56 

400 

250 

108 

78 

37-42 


500 

180 

56 

270 

220 

103 

73 

42-47 


625 

195 

56 

220 

200 

98 

68 

47-52 


775 

210 

56 

200 

200 

93 

63 

52-57 


1200 

240 

56 

150 

150 

88 

58 

57-62 



260 

56 

150 

150 

83 

53 

62-67 



280 

56 

150 

150 

78 

48 

67-72 



300 

56 

150 

150 

Limiting 








Outer 

Temper¬ 







Temp. 

ature 







Oth¬ 

Rub¬ 

Range of 

No. 900,000 C. M. 

Cable in Air 

Cooling Load; 

er 

ber 

Wire 

Heating load; amperes 

Amperes 

Ins. 

Ins. 

F. 

600 750 

900 

1200 

1800 

300 

0 

123 

93 

22-27 

720 

330 

120 

58 

660 

480 

118 

88 

27-32 

1035 

400 

130 

58 

500 

320 

113 

83 

32-37 

2400 

525 

140 

58 

420 

275 

108 

78 

37-42 


630 

150 

58 

300 

200 

103 

73 

42-47 


800 

160 

58 

250 

175 

98 

68 

47-52 


1100 

170 

58 

200 

175 

93 

63 

52-57 



180 

58 

175 

175 

88 

58 

57-62 



200 

58 

175 

175 

83 

53 

62-67 



220 

58 

175 

175 

78 

48 

67-72 



250 

58 

175 

175 



ELECTRICAL TABLES AND DATA 


357 


Table CLIII 


Open Wires 


Limiting 
Outer 
Temp. 
Oth- Rub¬ 
er ber 
Ins. Ins. 

Temper¬ 
ature 
Range in 
Conduit 

F. 

No. 1,000,000 C. M. Cable in Air 
Heating load; amperes 

650 812 975 1300 1950 

123 

93 

22-27 

720 

330 

120 

58 

118 

88 

27-32 

1035 

400 

130 

58 

113 

83 

32-37 

2400 

525 

140 

58 

108 

78 

37-42 


630 

150 

58 

103 

73 

42-47 


800 

160 

58 

98 

68 

47-52 


1100 

170 

58 

93 

63 

52-57 



180 

58 

88 

58 

57-62 



200 

58 

83 

53 

62-67 



220 

58 

78 

48 

67-72 



250 

58 


Cooling Load; 
Amperes 
325 0 

660 480 
500 320 
420 275 
300 200 
250 175 

200 175 

175 175 

175 175 

175 175 

175 175 


INDEX TO TABLES 

PAGE 

Aluminum and copper wire comparison. 8 

Arc lamp data. 10 

Armored cable data. 11 

Belting data. 19 to 23 

Bus bar data. 27 

Centigrade and Fahrenheit comparison. 32 to 33 

Center of distribution data. 30 

Conduit size recommendations. 35 to 37 

Conversion, inch to decimals. 329 

Cutout locations. 25 

Cutout dimensions . 44 to 47 

Electrolysis . 57 to 58 

Economy of conductors. 309 to 310 

Economy of motors. 163 to 164 

Elevator H. P. requirements. 67 

Fusing currents . 80 

Fusing transformers . 77 

Fuse Wire. 78 to 79 

Gauges, comparison of. 82 to 83 

Guying . 172 

Heating . 97 to 100 

Illumination. 105 to 114 

Insulator dimensions . 118 to 121 

Lamp renewals . 117 

Logarithms . 126 

Machinery, power determination for. 160 

Magnet calculations . 61 to 65 

Melting points ...*. 131 

Meters, maximum demand. 140 

Motor speeds, a. c . 145 

Motor wiring tables. 287 to 293 

Nails, dimensions of. 165 

Overhead const, data. 170 to 175 

Panel board dimensions. 178 to 180 

Pumping . 183 to 185 

Reciprocals of numbers. 187 to 190 

Reflectors . 191 


358 








































ELECTRICAL TABLES AND DATA 


353 


PAGE 

Ropes . 200 to 201 

Screw data . 205 

Sign hanging. 208 to 210 

Sign letters . 207 

Sparking distances . 215 

Switches, dimensions of. 224 to 231 

Terminals, dimensions of. 237 to 238 

Transformer distribution. 256 

Transformer efficiency . 258 

Trolley losses . 260 

Ventilation . 271 to 274 

Wires, aluminum . 316 to 321 

“ calculations . 285 to 300 

carrying capacity N. E. C. 282 

** “ “ combined . 284 

<< ** li underground . 265 to 268 

tt *t ** for snort periods. 330 to 357 


< t 
f ( 

< < 
<« 
4 4 
i 4 
4 4 
4 4 
4 t 


copper . 

copper clad. 

German silver. 

mains and branches. 

outside dimensions of. 

quantity required . 

reactances and resistances.278, 

sag and breaking strain. 

telegraph and telephone. 


311 to 315 
322 to 323 

324 
222 

326 to 328 
218 

297 to 299 
170 

325 







































WIRING DIAGRAMS 

AND 

DESCRIPTIONS 






















TABLE OF CONTENTS 


CHAPTER I. 

Call Bell Circuits, Bells, Dynamo Connections 

CHAPTER II. 

Annunciator Circuits. 

CHAPTER III. 

Fire and Burglar Alarms. 

CHAPTER IV. 

Telephone and Telegraph Circuits .... 

CHAPTER V. 

Electric Gas Lighting • 

CHAPTER VI. 

Primary and Secondary Batteries .... 

CHAPTER VII. 

Connecting Up, Locating Trouble .... 

CHAPTER VIII. 

Miscellaneous. 

CHAPTER IX. 

Electric Lighting. 

CHAPTER X. 

Arc Lamps, Nernst Lamp, Cooper Hewitt Lamp 

CHAPTER XI. 

Recording Wattmeters 


Page 

7 

21 

28 

43 

61 

66 

76 

86 

97 

116 

125 





TABLE OF CONTENTS 




CHAPTER XII. 

Direct Current Motors. 


• o 

Page 

131 

CHAPTER XIII. 

Automobiles, Charging Stations, Gas Engines 

• • 

159 

CHAPTER XIV. 

Direct and Alternating Current Generators, Com¬ 
pensators, Arc Lamp Control for Motion Picture 
Work . 

167 

CHAPTER XV. 

Alternating Current Motors, Transformers 

• 

• • 

196 

CHAPTER XVI. 

Armatures. 



233 

CHAPTER XVII. 

Switchboards, Ground Detectors . . . 

# 

• • 

236 

CHAPTER XVIII. 

Storage Batters Connections .... 

• 

• • 

250 

CHAPTER XIX. 

Testing .......... 

• 

• • 

259 

CHAPTER XX. 

Light . . 



273 

CHAPTER XXI. 

Wiring Tables. 

• 

• • 

277 

CHAPTER XXII. 

Electric Signs, Flashers, Display Lighting 

• 

• • 

285 





MODERN 

WIRING DIAGRAMS AND DESCRIPTIONS. 


CHAPTER I. 

CALL BELL CIRCUITS.-BELLS. DYNAMO CONNEC¬ 

TIONS. 


Figure 1 shows a simple bell circuit with extra 
res for a door opener to be operated from the vicin¬ 



ity of the bell. In this diagram the wire A may be 
left out and two ground connections used as shown 

at E. 


r , l , h 

A 

FIGURE 2. 




Figure 2 shows a method of wiring usually em¬ 
ployed where it is desired that parties at either end 




























8 


WIRING DIAGRAMS 


may call and also receive an answering ring as an 

indication that the signal has been heard. 

« 

Figure 3 shows another method of wiring to ac¬ 
complish the same purpose as the foregoing figure. 
In this case the bells are in series. This method re¬ 
quires greater battery power and one of the bells 
must also be arranged to act single stroke. 

Two ordinary circuit breaking bells will not act 
well in series as for instance the one having the stiffer 
spring or slightly weaker magnet would always lag 



me: 


A 

FIGURE 3. 



behind the other never coming to a full stroke. The 
advantage of this arrangement is that it enables 
the caller to know (by the ringing of his own bell) 
that the one at the other end is ringing. If the 
single stroke bell is located at the employer’s end 
and the circuit breaking bell at the attendant’s end 
the employer may know absolutely that the bell at 
the other end rings when the one at his station does, 
since it is the attendant’s bell which breaks the cir¬ 
cuit and causes the one at his own desk to ring. At 
one station (which may b^ taken as the attendant’s) 



















CALL BELL CIRCUITS 


9 


there is shown a 3-way switch by which the attend¬ 
ant n ay change his bell from vibrating to single 
stroke. This will enable him to arrange so that the 
bell may attract general attention or that it may be 
noticed only by one near it. 



Figure 4 shows one bell arranged to be rung from 
two stations. From one of the stations it will act 
single stroke and the ringing will indicate which 
station is calling. 





FIGURE 5. 


i*llh 

•I'H 


Figure 5 shows a number of bells arranged to be 
rung from one push button. With this method it is 
essential that the battery be of low internal resist¬ 
ance and of ample current capacity. This result 
may be obtained by grouping the cells as shown in 
the figure; it is, however, preferable to use large 
cells singly rather than smaller ones in multiple. 




























10 


WIRING DIAGRAM? 


Figure 6 shows connections by which either of the 
right hand pushes will ring the single bell near bat¬ 
tery, while from the station at battery the other two 
bells may be rung with one push button. 


r~y 



FIGURE 6. 


Figure 7 shows two bells arranged with one wire 
and grounds so that parties at either end may call. 
This method is economical in regard to wire but re¬ 
quires a battery and 3-way push at each end. The 
push buttons must normally keep the line closed 
from bell to bell, leaving the battery circuits open. 
When a push button is pressed the battery at that end 
rings the bell at the other. 



Figure 8 shows a bell so connected that it may be 
controlled from either of two stations. If both 
switches are set to the same wire the bell rings. If 













































CALL BELL CIRCUITS 


11 


either switch is moved to the other wire the bell 
stops. The advantage of this method lies in the fact 
that the bell may be left to ring continuously or 
not as desired. At one station the wiring is arranged 



for a double throw knife switch and at the other end 
for a 3-way snap switch. 

Figure 9 shows an arrangement of switches which 
enables one to turn the bells on or off at any one of 
any number of stations. These bells are in series and 



mav be left to ring continuously or not as desired, 
in this diagram throw-over knife switches, snap 
switches and specially designed switches are shown 
tc illustrate the different ways of attaining the same 
object. 














































12 


WIRING DIAGRAMS 


Figure 10 shows two bells connected by means of 
the switch S so that either may be used alone or both 



FIGURE 10. 


together. With the switch as shown b will ring 
alone. If the switch is turned to 2 and 2' both bells 

& 




FIGURE 11. 

will be in series, one acting single stroke. With the 
switch connecting 1 and 1' a will ring alone. 























































































































CALL BELL CIRCUITS 


13 


Figure 11 shows the manner of wiring commonly 
used in connection with speaking tube systems. 
It may also be used with interior telephones. Any 
station is able to call and may also be called from 
any other station. Only one battery is used and 
from one of its poles one wire connects to all of the 
push buttons. From the other pole another wire 
passes to one binding post of each bell. From the 
other binding post of each bell wires are then run 
to the corresponding push buttons at each of the 
other stations. 

Figure 12 shows an arrangement of wiring often 
used in connection with flat buildings. One set of 
push buttons is arranged at the main entrance on 
first floor usually together with letter boxes and 
speaking tubes. Another set of push buttons may 
also be placed one at the front door of each flat. 
This enables the bell to be rung either from main 
entrance or from entrance to flat. In addition to 
these, three different connections are shown in the 
three flats. In flat 1 a buzzer has been added and 
is connected to ring from rear door. In flat 2 the 
same bell rings from main hall, front door and rear 
entrance. In this case small signs requesting pai- 
ties to ring a certain number of times will be found 
very useful at front and rear doors. In flat 3, buzz¬ 
er and bell will ring from main entrance; the buzzer 
alone will ring from rear entrance and the bell alone 


14 


WIRING DIAGRAMS 


from front entrance. Three-way pushes are used 
for front and rear door. 

Figure IS shows the plan of a differential bell. The 
two coils are wound to oppose one another, so that 
when current is flowing through both there will be 
no magnetism. When current is applied at first it 
flows through one coil only; this attracts the arma¬ 
ture, which in turn closes the circuit through the 
other coil. Both coils now balance, and the armature 
is released, thus producing the same vibrations as in 
an ordinary bell. 



FIGURE 13. 



FIGURE 14. 


Figure 14 shows a short circuit bell. The cur¬ 
rent in its circuit is never broken, but, as the mag¬ 
nets attract the armature, the spring in connection 
with it closes the shunt circuit and this deprives the 
coil of current, thus destroying its magnetism and 
releasing its armature. This, and also the differen- 








































CALL BELL CIRCUITS 


15 


tial bell, will operate with less sparking than an 
ordinary vibrating bell, and both are useful on cir¬ 
cuits of higher voltage. The short-circuit bell 
should be used only on circuits where other resist¬ 
ances prevent any great rise in current. On an 
ordinary battery circuit it would not be useful. 

Figure 15 shows a bell arranged to act either 
single stroke or vibrating. For temporary purposes 
a bell may be made to act single stroke by simply 
adjusting the vibrator spring so that it does not 
open the circuit. 



FIGURE 15. FIGURE 16. 


Figure 16 shows a bell with continuous ringing 
attachment. As the armature is attracted the lever 
falls and completes the circuit through binding post 
< 2 . From this post a wire leads to the battery and 
completes the circuit through post 1. This attach¬ 
ment may be added to any of the other bells. The 









































16 


WIRING DIAGRAMS 


bell will continue to ring until the little lever is 
placed in its normal position. 

Figure 17 shows the arrangement of a polarized 
bell. This bell may be used in connection with al¬ 
ternating currents, and is the type generally used in 
telephone work. This type of bell may also be used 
with continuous currents when provisions for revers¬ 
ing are made; and in this way can be made to act 
as a single stroke bell, each reversal of current caus¬ 
ing one stroke. 



FIGURE 17. 


It is often desirable to operate bells from electric 
light circuits, either direct or through suitable stor¬ 
age batteries. For this purpose incandescent lamps 
may be placed in series with the bell system, and 
by choosing lamps of the proper candle power and 
voltage any necessary current may be obtained. There 
are also special resistances designed for this purpose 
which may take the place of lamps shown in diagram 
or may be placed one with each bell. The main ob¬ 
jection to lamps as shown in the diagrams would 




























CALL BELL CIRCUITS 


17 


be encountered when several bells in a system are to 
be used at the same time; since only a certain amount 
of current can pass through the lamps, only one bell 
at a time can be arranged to work properly. This 
trouble can be avoided by placing a lamp or resist¬ 
ance in series w T ith each bell and leaving out those 
shown in diagrams. One lamp on one side of the 
circuit is sufficient to insure proper operation, but 
it is advisable to use one on each side, as shown in 
the figure, to prevent serious damage which might 
be caused by grounds if one side only contained re¬ 
sistance. 

If dynamo current is to be brought into connec¬ 
tion w T ith bells, the wiring and insulation should be 
fully equal to that required for incandescent wiring. 
Push-buttons should be mounted on fireproof bases 
and no inflammable material should be used either 
within or about the bells. 

When the ordinary incandescent lamp is used for 
resistance, it must be borne in mind that the resistance 
of the lamp when cold is very much greater than 
when hot or burning; varying in the ordinary 110 
volt 16 c. p. lamp from 900 ohms cold to 220 ohms 
hot. If the lamp is to be used in a circuit where the 
current is \ow the cold resistance must be figured, but 
if the current approaches that at which the lamp 
burns the hot resistance must be figured, otherwise 
the rise in current when the lamp heats might dam¬ 
age the instruments in the circuit. To overcome this. 


18 


WIRING DIAGRAMS 


special lamps are made to be used on circuits where 
the current is low. 

In Figure 18 an arrangement is shown by which 
the battery is automatically disconnected when the 



FIGURE 18. 


dynamo is in operation. The magnet when energized 
attracts its armature, thus breaking the battery cir¬ 
cuit and completing the dynamo connections to the 
bell system. When the dynamo current ceases a 
spring draws the armature back again, closing the 
battery circuit. 



Figure 19 shows two batteries, each provided with 
a throw-over switch. While one is operating the 
bells the other is charging. The dynamo current 


























































CALL BELL CIRCUITS 


15 

never comes in contact with the bell wiring and no 
extra insulation is necessary. The + P°^ e the 
dynamo must connect to -f- pole of battery always, in 
order to charge. 



FIGURE 20. 


Figure 20 shows dynamo connections direct to the 
bells and a primary battery provided to operate bells 
when dynamo is at rest. 



FIGURE 21. 


Figure 21 also shows direct dynamo connection to 
the bell wiring. In this diagram a master circuit 
breaker in the form of a buzzer or bell is introduced 
into the circuit, and the bells throughout the build¬ 
ing may be arranged single stroke. The sparking 
is always more destructive with high potential, and 
often causes much trouble with ordinary cheap bells; 
therefore this circuit breaker should be of high grade 









































20 


WIRING DIAGRAMS 


and located convenient to engineer or janitor, so it 
may be kept in order. This circuit breaker should 
also be selected with reference to the bells used, as it 
must not vibrate faster than the natural vibration 
of the bells. 


CHAPTER II. 


ANNUNCIATOR CIRCUITS. 

Figures 22, 23 and 24 show diagrammatical rep¬ 
resentations of ordinary annunciators. In Figure 22 
two annunciators are shown, one to be located in the 
kitchen or hall and the other perhaps in the servant’s 
bedroom. By means of the switches 1, 2, 3, the push 
buttons are connected to either one of the annuncia¬ 
tors as may be desired. The bell connected with each 
annunciator has a continuous ringing attachment 
shown by the extra wire attached to the middle bind- 



FIGURE 22. 


ing post. The overthrow switch S is not absolutely 
necessary but is quite desirable as a safeguard; it 
sometimes happens that the continuous ringing at- 

21 




















































22 


WIRING DIAGRAMS 


tachment falls, and without this swdtch the bell would 
ring and run battery down, even though the annun¬ 
ciator were disconnected by the switches 1, 2, 3. 



FIGURE 23. 


Figure 23 shows a method of connecting two an¬ 
nunciators which should be avoided. With just the 
right battery strength and accurate adjustment of 
drops it may work fairly well for a time, but sooner 



or later it will result in confusion. By tracing out 
the circuits it will be seen that from any push there 
are several paths which the current may take although 
one is more direct and has less resistance than the 
others. 




















































































ANNUNCIATOR CIRCUITS 


23 


Pigure 24> shows an annunciator to which have 
been added the switches 1, 3, and also the wires 

leading to the three bells shown below it. The switches 
are mechanically connected so that all may be oper¬ 
ated at once. These switches serve to disconnect the 
annunciator magnets and at the same time to con¬ 
nect the three bells with the push buttons. With the 
switches set to the magnets, the current from any 
push button passes through the corresponding mag¬ 
net and through the single bell at the right. With 
the switches set to the wires leading to the bells the 
current passes through the corresponding bell without 



FIGURE 25. 


disturbing the single bell. The three bells shown to¬ 
gether are of different sound and the ring will indi¬ 
cate location of the caller without the necessity of 
looking at the annunciator. This may be useful in 
















































24 


WIRING DIAGRAMS 


many residences where the room in which the annun¬ 
ciator is located is not always occupied. 

Figure 25 shows a return call annunciator system 
as it is frequently used in hotels, where it is neces¬ 
sary that a guest may call the office as well as be 
called from the office. This system requires one bat¬ 
tery and two leading wires for each room, one leading 
wire passing from each room to the annunciator, while 
another passes from each push to one of the bells lo¬ 
cated in rooms. 



Figure 26 shows another system of annunciator 
wiring for the same purpose as Figure 25. This 
system requires only one leading wire from each 
room, but two general battery wires. One battery 
wire leads to each bell and to the annunciator, while 





































ANNUNCIATOR CIRCUITS 


25 


the other leads to one point of each push button. 
Three-way push-buttons are used in the rooms and 
at the annunciator. Pressing any of the buttons 
1, 2, 3, will operate the annunciator, while pressing 
any of the buttons at the annunciator will ring the 
bell in the corresponding room. 



FIGURE 27. 


Figure 27 shows diagrammatically the wiring used 
in the Partrick, Carter & Wilkins annunciator system, 
which is quite extensively used. Two general battery 
wires are necessary, and also one wire from each room 
to the corresponding drop on the annunciator. Two 
three-way pushes, one at the annunciator and one in 
each room, are also necessary. These push-buttons 
are mounted on bells and on annunciator respectively, 
making the whole arrangement very compact. With 
reference to each other, the polarities of the two sets 
of batteries must be as shown. If it were otherwise 



















































26 


WIRING DIAGRAMS 


both batteries, acting in series, would ring all of the 
bells and attract all of the annunciator needles when¬ 
ever the two push-buttons on the same wire were 
pushed at the same time. This will, however, very 
seldom occur. By means of the dotted lines at 1 and 
<2 the circuits thus formed can be readily traced. 



The annunciator magnets used in this system are 
made so as to partially retain their magnetism after 
the current ceases to flow, in order to hold the indi¬ 
cator until an attendant releases it. The magnets 
are magnetized in a certain direction before the an¬ 
nunciator is sent out, and it is advisable to connect 
the battery so that this magnetism is not reversed. 




























































ANNUNCIATOR CIRCUITS 


2 1 


The binding post on annunciator to which the zinc 
pole of battery should be connected is plainly indi¬ 
cated on each instrument. 

It must not be understood that the P., C. & W. 
annunciators can be used with this method of wiring 
only; in fact, either of the methods shown in Figures 
25 or 26 are applicable to it, Figure 25 being pre¬ 
ferred where it is likely that at some time telephones 
may be connected with it. 

Figure 28 shows an arrangement of annunciators 
which is quite economical in hotels or restaurants, 
where there is a great variation in business at differ¬ 
ent hours. Each floor has an annunciator which in¬ 
dicates the room sending a call, and each of these 
annunciators is in series with one drop of another 
annunciator located at the main office and w r hich indi¬ 
cates the floor from which the call came. The bells 
located with annunciators on the different floors are 
each provided with a switch, by which any one of 
them may be made to act single stroke or be cut out 
altogether. During busy hours an attendant is kept 
on each floor and the bells are set to act independent¬ 
ly, wdiile the annunciator and bells at the main office 
are cut out altogether by the switch shown. During 
slack hours the bells on the different floors may be 
cut out and an attendant stationed at the main office 
only. The figure show's switches by which the bell® 
may be .cut out. 




CHAPTER III. 


FIRE AND BURGLAR ALARMS. 

Figure 29 shows a number of annunciators ar¬ 
ranged to act as a manual fire alarm. When any one 
of the switches S is closed it causes a bell to ring 
on each floor, and each annunciator indicates from 
which floor the alarm came. Independent batteries 
are provided for each floor to insure greater relia¬ 
bility, as one battery failing will disable one floor 
only. The batteries must all be arranged as shown in 
diagram, so that all will send current in the same di¬ 
rection. 

Figure 30 shows the building system of the Con¬ 
solidated Fire Alarm Telegraph Company, of New 
York, and the description here given is condensed 
from a memorandum furnished by this company to 
the Underwriters’ Bureau of Fire Engineering, and 
which forms part of Electrical Signal Report No. 14. 

The house wiring used with this system consists 
entirely of two parallel circuits led throughout the 
building in close proximit} r . At suitable intervals, 
as required by the local insurance boards, thermo¬ 
stats, c, and manual switches, D, are installed. The 
current flows continuously through both circuits, in- 
eluding the magnets A and B. The magnet A while 

28 


FIRE AND BURGLAR ALARMS 


29 


energized holds at rest a transmitting device which, 
when released, automatically causes a fire signal to be 
sent in. 



In order to send in a fire signal, it is necessary that 
both coils of magnet A be de-energized; this will oc- 









































































































































































30 


WIRING DIAGRAMS 


cur only when both lines are broken, either through 
the melting of a fuse in each line, or by means of 



one of the manual switches. The two coils of magnet 
B are wound in opposite directions, and hence there 














































































































































FIRE AND BURGLAR ALARMS 


31 


is no magnetism while current flows equally in both 
lines. Should, however, any variation in current 
strength occur in either of the lines the balance is at 
once destroyed, and the armature being now attracted 
releases a transmitting device which sends in a trouble 
alarm. In order that any possible electrical defect 
may disturb the balance of the magnet B and send 
in a trouble alarm, the battery in one of the lines is 
of higher voltage than the other. The resistance of 
the magnets and lines vary in the same proportion, 
so that normally the current in both lines is equal. 
Part of the transmitting devices are shown at M and 
M'. The double contact springs L and L' normally 
keep the outside circuit X-Y closed. The springs M 
and M' are provided to connect the ground E by 
means of projections on the contact wheels, whenever 
the double contact springs close on any of the other 
projections. In this way, by means of the ground, 
signals are transmitted, even though the circuit X-Y 
be broken somewhere. 

In view of the importance of the grounds E and P, 
they are placed under constant test by means of the 
battery O, which maintains current from E to P 
through the relay N. If this current fails, the arma¬ 
ture of N short-circuits the main wires, causing a 
trouble call to be sent in. Whenever a fire alarm oc¬ 
curs the transmitting device revolves the cylinder G. 
This cylinder, by means of raised teeth, engages the 
contact springs of wires led to it from the different 


32 


WIRING DIAGRAMS 


floors, and in this way controls the magnet in the an¬ 
nunciator H, which moves the pointer forward one 
step for each impulse received. When a point be¬ 
yond the broken line is reached, the impulses cease 
and the pointer stops, indicating the location of the 
fire. The cylinder G is so arranged that the local 
ringing circuit is closed only when a fire alarm is 
sent in. 



Figure SI shows an annunciator arranged as a 
burglar alarm. When used for this purpose it is 
usual to have the bell arranged to ring continuously 
when once started. It is also necessary to arrange 
for what is known as the silent test. For this purpose 
each circuit leaving the annunciator is provided with 
a switch by which it may be disconnected during the 







































FIRE AMD BURGLAR ALARMS 


33 


day to avoid giving an alarm whenever a door or win¬ 
dow is opened. When ready to close the house at 
night the switch S is turned to connect at 1; each 
circuit is then thrown in singly, and if any door or 
window has been left open the drop will indicate it 
without ringing the bell. When all is in order the 
switch is turned to 2, thus completing the circuit 



through the bell. The dotted lines show the wiring 
for the continuous ringing attachment as shown in 
Figure 16, Chapt er I. 

With burglar alarm systems it is quite usual to 
connect the wiring through a suitably arranged clock, 
which can be made to connect or disconnect the wiring 
at certain hours. Provision may also be made by 
which the current, when releasing the annunciator 


















































34 


WIRING DIAGRAMS 


drop, also releases a weight or spring, allowing them 
to operate a mechanical bell. 

Figure 32 shows the same annunciator and bell 
arranged to act as a combination burglar alarm and 
house annunciator. The same provision for silent 
test has been made as in Figure 31. The solid lines 
show the wiring for window and door springs, while 
the dotted lines indicate wiring to push buttons. By 
means of the four switches shown on the annunciator, 
the window and door circuits may be shut off during 
the day, leaving only the push buttons connected. 
The push buttons are always in circuit, so that an 
alarm may be turned in at any time. 

In this figure an extra bell is shown, which may be 
connected in series with the annunciator bell by mov¬ 
ing the switch S to point 3. In this case the current 
entering through any drop of the annunciator will 
pass through both bells and the magnet R to point 3, 
switch S and the battery. Current passing through 
R attracts the armature A, allowing the switch to 
drop, thus closing the battery circuit through both 
bells, causing them to ring continuously. The extra 
wiring for this purpose is shown in dotted lines. 

Figure 33 shows an attachment for constant ring¬ 
ing which is known as Callows. This consists of a 
magnet provided with two coils as shown. When the 
button is pressed current passes around coil 1, and 
this attracts the armature A, which is also in electrical 
connection with the battery. A part of the current 


FIRE AND BURGLAR ALARMS 


35 


now passes along the armature to the wire leading to 
the bell, and at the junction X it divides, one-half 
passing through the bell and the other around coil 2 
of the magnet. The current passing around coil 2 





FIGURE 33. 

keeps the armature in position while the current in 
the bell is interrupted. If the switch S is open the 
bell will ring only while the button is pressed. With 
this attachment the switch controlling the constant 
ringing may be at any distance from the bell. 



Figure 34 shows a closed circuit burglar alarm. 
Current is always flowing along the mam line. This 
current, by means of relay R, keeps the local bell cir- 


























































36 


WIRING DIAGRAMS 


cuit open. Whenever the main circuit is opened any¬ 
where the relay armature A flies back, closing the 
local circuit and causing the bell to ring. This figure 
also shows combination wiring, whereby the bell may 
be used single stroke for calling. Switches are pro¬ 
vided at 1, £ and 3, and arranged so that connection 
is made with the circuit shown in dotted lines before 
that in the full lines is broken. While current passes 
along the wires shown in full lines it passes through 
the relay only. When one of the buttons makes con¬ 
nection with any of the wires shown in dotted lines, 
the current passes through the bell and relay. The 
bell is arranged single stroke for calling, but will 
ring vibrating when the relay closes the local circuit. 



Figure 35 shows a simple closed circuit burglar 
alarm. In this case the current passes continuously 
through the bell magnets and keeps the bell arma¬ 
tures attracted. In this way the local circuits B', B r/ 
are kept open as long as current from the closed cir- 





























FIRE AND BURGLAR ALARMS 


37 


cuit battery B flows through the magnets. When¬ 
ever the main wires are opened both bells will ring 
continuously. Short-circuiting the main wires will 
also cause one or both bells to ring, according to loca¬ 
tion of the short circuit. This is a very simple and 
useful arrangement, and may be extended to any 
number of bells in a building. 

If crow foot batteries are to be used in connection 
with this system the bells must be specially wound; 
the ordinary bell has not a sufficient number of turns 
of wire to operate properly with the small currents 
obtainable from these batteries. 



Figure 36 shows a burglar alarm system using 
both open and closed circuits. Both circuits are run 
to each opening. The wiring is the same as in 1 igure 








































































38 


WIRING DIAGRAMS 


31, and the three closed circuits passing through the 
three relays, 1, 2, 3, have been added. While current 
passes through these relays their armatures are at¬ 
tracted; if any circuit is opened the corresponding 
armature flies back and closes the circuit through the 
corresponding drop on the annunciator. This system 
requires a closed circuit battery, and, when certain 
kinds of cells are used, provision must be made to keep 
the battery at work if the annunciator is disconnected 
for any great length of time. As here shown, the 
battery will always be at work unless a window or 
door in each section is open. 



FIGURE 37. 


Figure 37 shows an annunciator as it may be used 
either as a fire or burglar alarm. By means of the 
magnet M, an electric circuit is closed whenever con- 













































































TIRE AND BURGLAR ALARMS 39 

tact is made by one of the push buttons or contact 
springs. With each electric light, L, an electric bell 
is placed, and whenever the alarm is set off bells will 
ring in the different sections and a general illumina¬ 
tion w T ill take place. The bells used for this purpose 
should be of the type shown in Figures 13 or 14, 
Chapter I, and should be carefully installed, so there 
may be no grounding or bad contacts. 

The electric light circuit here shown may be added 
to any of the closed or open circuit burglar alarm 
systems described by simply arranging a magnet like 
M, which, by attracting or releasing its armature, 
allows the switch S to fall and close the electric light 
circuit. Any burglar alarm annunciator may also be 
used as a fire alarm if suitable thermostats are con 
nected with the w r iring, arranged to open or close the 
circuit when the temperature rises above a certain 

point. 

Figure 38 shows a system of burglar alarm wiring 
which can be used when some special object is to be 
protected. This object may be a safe, vault or room, 
and may be located any distance from the alarm sta¬ 
tion. 

In the diagram C is a coil of any chosen resistance, 
which is to be placed inside the object to be protected. 
By tracing the circuits it will be seen that current 
from battery B, which is a closed circuit battery, 
flow's through this coil and through a closed circuit 


40 


WIRING DIAGRAMS 


burglar alarm spring G, thence through magnet R' 
back to battery. 

Another circuit running from the same battery 
goes through magnets R r/ and M, back to battery. 
When current is flowing from battery B the armature 
E is held in a balanced position midway between R' 
and R" (this is facilitated by means of springs as 
shown), and the armature A is attracted. This holds 



the local bell circuit open. If the line running to C 
is opened, the current through R' ceases, and it be¬ 
comes demagnetized. The armature is then attracted 
by magnet R" and the bell circuit is closed at F. If 
the line running to C is short-circuited, the increased 
current in R' attracts the armature and the bell cir¬ 
cuit is closed at F r . If for any reason the battery B 

























































F'IRE AND BURGLAR ALARMS 


41 


gives out, the magnet M is demagnetized and the 
armature A closes the bell circuit. t When alarm is 
not in use the switch S is thrown over, opening the 
alarm circuit. This device was designed and patented 
by G. B. Lehy, of Medford, Mass. 



Figure 39 shows the wiring of a burglar alarm in 
which both closed and open circuits are used. Cur¬ 
rent from the closed circuit battery A flows continu¬ 
ally through wires 1 and 3 and the magnet M. If 
this circuit is broken the armature of M falls and 
closes the bell circuit; this rings the bell by means of 
the open circuit battery B, and keeps it ringing con¬ 
tinuously. If any of the springs between 1 and 2 
are brought together, both batteries will work through 

the bell in series. 













































42 


WIRING DIAGRAMS 


In systems of this kind the wires may be twisted or 
braided into cables, and it will be very difficult to de¬ 
termine which wires must be short-circuited or cut in 
order to make the alarm ineffective. The switch S is 
provided to cut the alarm bell in or out of use as de¬ 
sired. 

This arrangement is taken from Max Linder’s book 
on “Haus Telegraphie,” and was devised by 0. 
Schoeppe, of Germany. 


CHAPTER IV. 


TELEPHONE AND TELEGRAPH CIRCUITS. 

Figure 40 shows diagrammatically the connections 
of an ordinary telephone instrument when in use. 
While the receiver R hangs on the hook, the line cir¬ 
cuit is complete through the polarized bell and mag¬ 
neto generator to ground. This is the connection 
when the instrument is not in use. T is the transmit¬ 
ter, and it is in series with a small induction coil and 


rWWM-f? 



FIGURE 40. 


battery, which is connected with the local circuit as 
shown; the local battery circuit being open when the 
telephone is not in use. The magneto generator is 
usually provided with a shunt circuit, which allows 
the calling currents from other stations to pass around 
it and ring the bell. The generator is so arranged 

43 






























44 


WIRING DIAGRAMS 


that this circuit is automatically opened when the han¬ 
dle is turned. 

Figure 41 shows the connections of the bridging 
bell system. In this system the bells are all in multi¬ 
ple and always in circuit. The resistance of the bell 
magnets is very high and the self induction quite 
great. This gives them sufficient impedance to pre- 


fkf 

J 


> o •a 

M 




FIGURE 41. 


vent telephonic currents from passing, but does not 
prevent the lower frequency currents of the magneto 
from ringing the bells. The magneto generator must 
be of sufficient capacity to ring all of the bells at the 
same time. This system requires some code of sig¬ 
nals, since all the bells ring whenever any station is 
called. 

Figure 4<2 shows a telephone line with the stations 
arranged in series. With the instruments here shown 
no induction coil is used, the talking batteries and 
transmitters being arranged directly in series with the 
teler>hone instruments. A signalling battery is re- 





























TELEPHONE CIRCUITS 


45 


quired at each station, and also a 3-way push. When¬ 
ever this push is pressed at any station all of the bells 
will ring. The number of stations that may be ar- 



FIGURE 42. 


ranged on a line of this kind is very limited, since the 
talking currents must pass through the bell magnets 
of all stations except those talking. 



In Figure 43 an’ intercommunicating system is 
shown using magneto generators for calling. Each 
of the stations 1, 2 and 3 contains the arrangement 






























































































































46 


WIRING DIAGRAMS 


shown in Figure 40. To call any station the plug 
is inserted in the jack which connects with the wire 
leading direct to the station wanted. On turning the 
generator the bells will ring, and upon taking up the 
receivers the line is ready for talking. 

Figure 44 shows an intercommunicating system 
using one common battery for signalling and indi¬ 
vidual talking batteries at each station. As in Figure 



FIGURE 44. 


48, the plug is inserted in the proper jack, and upon 
pressing the 8-way push the bell at the corresponding 
station will ring. The bell at the calling station will 
not ring. 









































































TELEPHONE CIRCUITS 


47 


With all systems such as these the plugs are likely, 
through carelessness, to be left in the jacks, and more 
or less confusion may result. To obviate this, special 
devices are made, to take the place of plugs shown 
here, and which automatically make the proper con¬ 
nections when the receiver is replaced. 

Figure 45 shows an ordinary annunciator system 
adapted for the use of telephones. Each station can 
communicate with the office only. A is the annuncia¬ 



tor receiving the signals from the different stations. 
By plugging in at the proper wire in B, and pressing 
the button any station may be called. W hen the but¬ 
ton is released the line is ready for talking if the re¬ 
ceivers are removed from their hooks. As here shown. 












































































48 


WIRING DIAGRAMS 


one common talking battery is used, and another bat¬ 
tery is used for signalling. 

In Figure 46 an adaptation for telephones of the 
annunciator system given in Figure 26 is shown. 
Whenever the plug is inserted in any of the jacks at 
B, it breaks the wire at this point, thus forming an 
independent circuit through the station called and the 



office instrument. With this system there is shown 
one common signalling battery for all stations and 
a talking battery at each station. 

It has not been thought necessary to give more 
than the foregoing diagrams in connection with tele¬ 
phones, as anything approaching a full exposition 
of the many different methods of connecting them 
would alone fill a volume. The foregoing diagrams 



































































TELEPHONE CIRCUITS 


49 


are sufficient to illustrate the methods usually em¬ 
ployed in house wiring. For a fuller treatment, and 
for illustrations of exchange practice, the reader is 
referred to the more pretentious works dealing with 
telephone practice only. 

As telephone receivers are very sensitive, it is es¬ 
sential that the wires connecting them should not be 
run very close to other wires carrying currents of 
electricity. To avoid cross talk and other disturbing 
influences, the lines should be arranged so that both 
sides are of equal length and resistance. Arrange¬ 
ments should be such that no electro-magnets are left 
in circuit when the line is used for talking. It is also 
advisable to cross wires or twist them together; this 
will help neutralize inductive influences. In factories 
and kindred places where there is much vibration, 
the telephone instruments may be suspended from 
springs. 

Figure 47 shows the connections of an ordinary 
long distance telegraph line with relays R and sound¬ 
ers S. The relays are used, because in long distance 
lines it has been found unprofitable to maintain cui- 
rents sufficiently strong to control the heavy arma¬ 
tures necessary on sounders to make the signals audi¬ 
ble. For this reason the relays are equipped with 
very light armatures, and control a local circuit which 
operates the sounder. One-half the battery is placed 
at each end of the line; this lessens the trouble from 
leakage. Each station is also equipped with a light- 


50 


WIRING DIAGRAMS 


ning arrester connected to ground, as shown, and a 
switch closing around the key. This applies to inter¬ 
mediate stations as well as end stations, and interme¬ 
diate stations are also equipped with a switch, by 



which they may be entirely cut out or connected to 
ground on either side, in case of a broken line or other 
trouble. 



FIGURE 48. 

In Figure 48 a very simple form of repeater is 
shown, which is due to Edison. It can be very readily 
set up, and requires no additional apparatus except 














































































































TELEGRAPH CIRCUITS 


51 


a 3-way switch shown in diagram. With the switch 
S, as shown, the current from the eastern line passes 
through both batteries to ground and keeps the arma¬ 
ture I attracted. At the same time current from the 
west passes through the armature I and the main bat¬ 
tery to ground. When the eastern circuit is opened, 
armature I is released and opens the western cncuit, 
thus repeating into it. With the switch turned to the 
other point, the western circuit will repeat into the 

eastern. 



In Figure 49 another form of repeater, known as 
Milliken’s,' is shown. This does not require the 
changing of any switch to make one circuit repeat 
into the other, but is entirely automatic. The cur¬ 
rent coming from the east normally keeps the arma¬ 
ture of magnet 1 attracted; this armature controls the 































































































52 


WIRING DIAGRAMS 


circuit of magnet 2. If, now, the current in the east¬ 
ern circuit is interrupted, the armature of 1 flies back, 
opening the local circuit of magnet 2; this in turn 
releases its armature and breaks the western circuit at 
A. The breaking of this circuit would result in re¬ 
leasing the armature of 4, but at the same instant the 
armature of 2 opens the western circuit it also opens 
the extra circuit controlling the magnet 3. This re¬ 
leases the pendant armature, which is drawn by its 
spring against the armature of 4 and prevents its 
opening the circuit. The west end station is an exact 
duplicate of the eastern, and when sending from that 
side the operation is repeated in a similar manner. 

THE TELAUTOGRAPH. 

An elementary diagram of the connections of the 
telautograph is given in Figure 49a and the complete 
connections showing switches, etc., in Figure 49b. 

The message to be transmitted is written upon the 
platen P, Figure 49b, by a pencil occupying the position 
shown as a black dot. The movement of the pencil, 
by means of light rods, moves the arms A, A', sometimes 
pulling one and pushing the other. These arms move 
over resistances and thereby vary the current strength 
in two lines which lead to the receiver shown in upper 
half of the figure. In the receiver each of the two 
magnets M, M', are fitted with plungers which are free 
to move up and down. These plungers are drawn up¬ 
ward by springs and sucked into the cores of the mag- 


TELEGRAPH CIRCUITS 


Si 






1 


FIGURE 49*. 

















































































































64 


WIRING DIAGRAMS 


nets by currents passing through the coils of the 
plungers. The magnets themselves are separately 
excited. 

These plungers connect to two arms similar in princi¬ 
ple to those of the transmitter and the nature of the 
connection is such that every motion of the pencil 
upon the platen P is reproduced by a similar pencil or 
pen designated by a black dot in the receiver. Thus 
the message written upon the transmitter platen is re¬ 
produced with great fidelity upon the platen of the 
receiver. 

The manner in which this is accomplished can best 
be explained by reference to the elementary diagram 
Figure 49a. When the instrument is in action current 
flows from the battery shown with the transmitter at 
the left, along the wires drawn as heavy lines, passing 
through the main magnets M, M', and the auxiliary 
magnets m, m'. The actual work of writing is done 
entirely by the currents passing over these wires. It 
will be seen that the arms A, A', as they move over the 
resistances cutting out or in resistance and also acting 
as shunts to each other, produce great variations in the 
current strength in the two transmitting lines. These 
changing currents affect the magnets M, M', correspond¬ 
ingly and reproduce the writing. 

In the transmitter is also included an induction coil 
I and its secondaries, together with an interrupter I'. 
The alternating currents produced by these coils are 


TELEGRAPH CIRCUITS 


55 



l^nT [ 



_ £X 


FIGURE 49b. 






























































































































































































































50 


WIRING DIAGRAMS 


superimposed upon the continuous currents in the 
main circuit. 

S is a small switch so connected that it is closed when 
the instrument is not writing. Pressure of the writing 
pencil upon the platen opens this switch and thereby 
strengthens the alternating currents. This increase 
in current strength operates the relay m in the receiver 
and causes it to open the circuit through the pen lifting 
magnet L. This releases the pen so that it becomes 
free to move in accordance with the arms of the re¬ 
ceiver. The arrangements are also (by vibration of 
armature of m) such that the alternating currents keep 
the pen in a slightly vibratory state and thus reduce 
friction to a minimum. When the pressure is with¬ 
drawn from the platen the alternating currents become 
too feeble to interfere with the continuous, the relay 
m again closes the circuit through the penlifter and 
the pen is raised. 

The object of m r in the receiver is to control the 
battery and the local circuits in the receiver. When 
its armature is attracted, the circuit through L, M, M', 
and O are closed. 

O is an electromagnetic device which shifts the 
paper when the circuit is broken at the end of a line. 
When no current is on the line, O keeps the contacts 
D closed. This places the bell E in parallel with M 
and m, and as these are of higher resistance than the 
bell, the latter rings whenever the push-button C is 
pressed. This is used merely for signalling. 


TELEGRAPH CIRCUITS 


57 


X-RAY CIRCUIT. 

A diagram of the wiring and instruments often used 
in connection with X-ray tubes is given in Fig. 49c. 
The tube itself is shown at T connected to the second¬ 
ary of a strong induction coil. At the terminals of 
this secondary winding of the induction coil an adjust¬ 
able spark gap G is provided. This is used to protect 
the tube against excess voltage. This gap properly 
adjusted will act as a shunt and the excessive current 
will jump the air between the spark points rather than 
pass through the tube. 



The exact nature of the light emitted depends some¬ 
what upon the degree of vacuum maintained in the 
tube. 

As a general rule tubes of low vacuum take more 
current, emit more light, and the light is of greater 
actinic power. 














































58 


WIRING DIAGRAMS 


The light emitted from a high vacuum tube, how¬ 
ever, is more penetrating, that is, will pass through 
greater opaqueness than the other. 

To obtain the best results in all cases, it is therefore 
advisable to have on hand a stock of tubes suitable 
for different kinds of work. 

The color of the light also varies somewhat with the 
nature of glass used. 

In order to properly operate the tube it is necessary 
to send a very rapidly interrupted current of elec¬ 
tricity at a very high voltage through it. This is done 
by means of a good induction coil which differs from 
the common form only in the nature of the interrupter. 

In the ordinary induction coil in which no particular 
attention is paid to the exact nature of the make and 
break, secondary currents are induced at time of make 
and also of break. 

An induced current is produced in the secondary 
whenever lines of force are increased or decreased in 
the winding or iron core. These secondary currents 
flow in one direction while the lines of force are in¬ 
creasing and in the opposite while they are decreasing. 
The value of the induced E. M. F. is in proportion to 
the rate of change of the lines of force. That is to say, 
if the current is increased from 0 to 10 amperes in 1 
second it will induce secondary currents with 10 times 
the E. M. F. as if it were increased the same amount 
in the time of 10 seconds. 

In the X-ray tube it is essential that the currents 
be practically all in the same direction and therefore 


TELEGRAPH CIRCUITS 


59 


one of the induced currents must be as far as possible 
eliminated. The E. M. F. induced at time of break 
of the primary current is much greater than that at 
make because the circuit may be very suddenly (prac¬ 
tically instantaneously) opened, while the make cur¬ 
rent rises comparatively slow to its full value. The 
break E. M. F. is therefore much greater than the 
make and it is the one that is used to produce the 
light. 

The greater the difference between the two the more 
desirable it is for if the make E. M. F. can be kept 
low enough it will not send current through the tube. 

The sparking which occurs at time of break of cir¬ 
cuit is the only element that prevents instantaneous 
break of current, and to reduce it as much as possible, 
for the double purpose of preventing destructive action 
and increasing the suddenness of the break the con¬ 
denser C is provided. Part of the current at time of 
break instead of continuing in the form of a spark 
rushes into the condenser to be discharged when the 
make occurs. 

There are three distinct methods of interrupting 
the current in use. One of these is the well known 
method employed with ordinary induction coils or 
vibrating bells. 

The second method is that of causing the interrup¬ 
tions to be made through a small motor which operates 
either a plunger or a disc with projections so arranged 
that they enter and leave a mercury contact with 
great rapidity. A motor is also sometimes employed 


60 


WIRING DIAGRAMS 


to throw a jet of mercury against a succession of con¬ 
tacts mounted on the inner periphery of a suitable jar. 

The third method is known as the electrolytic. 
This is an arrangement very similar to a battery. 
The positive pole of the circuit is connected to one of 
the poles of the break (which is platinum) and the 
other pole of the break is a lead plate. Diluted sul¬ 
phuric acid is also used. As current passes through 
this cell bubbles are formed on the platinum and these 
stop the current flow by their resistance. They im¬ 
mediately pass away and the current begins to flow 
again. The interruptions produced in this way are 
much more rapid than those of any other method and 
this method can also take care of much stronger cur¬ 
rents. These breaks are simple and easily kept in 
order. Always make the platinum the positive pole, 
if otherwise it will soon be destroyed. 

It is important to arrange that current cannot be 
turned on to the induction coil unless the interrupters 
are in action or ready to act. For this reason where 
motor drive interrupters are used the switch S may be 
arranged to close the motor circuit before the circuit 
to the coil is closed. 

By means of the shunt resistance connected as shown 
any desirable voltage is obtainable from a 110 volt 
circuit. Start with low voltage and work up to de¬ 
sired voltage. 

If an alternating current is to be used it must be 
rectified by motor generator or some other means. 


CHAPTER V. 


ELECTRIC GAS-LIGHTING. 

Figure 50 shows the wiring of a complete metallic 
return gas-lighting system. I is the spark coil, which 
is absolutely essential. This spark coil has a relay 
attachment, R, which closes the bell circuit whenever 
the spark coil is energized. Should a ground or short 
circuit occur on the system, the bell will immediately 



call attention to it. By means of the switches S the 
system is divided into a number of circuits, and, by 
disconnecting the circuits, one at a time, the one out 
of order may be readily found. 

For so-called automatic burners it is necessary to 
run two wires to each burner; and push buttons con- 

61 















































62 


WIRING DIAGRAMS 


trolling one burner may be placed in different parts 
of the building, as shown at top of figure. With 
pendants the gas can be controlled at the fixture only. 
Automatic burners are not very safe, as there is al¬ 
ways a liability of gas leaking. 

If a cheaper installation than the above is desired, 
the rela} r , bell, and switches S may be omitted, and 
the whole installation arranged as one circuit. The 
gas piping can also take the place of the return wire. 
Instead of employing a separate battery to operate 
the tell-tale bell, two cells of the main battery may 
be used; as the cells so used, however, give out much 
earlier than the others, it is not considered good prac¬ 
tice to do so. 



FIGURE 51. 


Figure 51 shows a method which allows of tw r o 
parties controlling one gas jet; the gas not being 
turned out until both parties are through with it. S 
and S' are two switches which can make connection 
with the current carrying wire 1. By turning the 
switch S or S' to this wire and pressing the proper 
button, the gas may be lit by either party. The first 
party to retire will press the off button, and finding 
no current will, after releasing the button, throw the 









ELECTRIC GAS-LIGHTING 


63 


switch S or S to the wire 1. This will give current 
to No. 52, and when the other party presses the proper 
button the gas will be turned off. This method pre- 
supposes that the switch S or S r is returned to its 
normal position after being used. 

Figure 52 shows a system of gas lighting with an 
induction coil. A spark of high potential is produced 
which can jump many small air gaps arranged above 
gas jets in series. With the switch one circuit at a 
time is ignited. In systems of this kind about 15 



FIGURE 52. 


burners are allowed to a 1 inch spark coil; i. e ., a 
coil giving a spark 1 inch in length. If possible, 
gas jets should be arranged so close together that 
they will light from one another. In such a case 
only a few of them need be equipped with spark cor 
tacts. Very high insulation is essential with this sy 
tern, and there may be but little use for it in these 
days of electric lighting. 

In Figure 53 are shown the connections used in 
the Edwards condenser system. Here all of the burn¬ 
ers are wired in multiple and each is equipped with 
a small condenser. This system is mentioned in Mr. 
H. S. Norrie’s work on gas lighting, and is said to 


























64 


WIRING DIAGRAMS 


be successful. A suitable induction coil is used, and 
it need not have a very great spark capacity, and 



FIGURE 53. 


there is much less danger of a breakdown in the in¬ 
sulation. 



Frictional gas lighting machines may also be used, 
and they are connected similar to Figures 52 and 53, 














































ELECTRIC GAS-LIGHTING 


65 


one terminal leading to ground or common return 
wire, and the other to the switch. 

As grounds and short circuits on gas lighting sys¬ 
tems are quite common, several forms of automatic 
cutouts have been devised. One of these is shown in 
Figure 54. The battery wire passes through a mag¬ 
net which controls clockwork connected with a long 
pinion shaft. This clockwork is started and continues 
in operation while current is passing through these 
magnet coils. If the current lasts only an instant 
there will be but very little movement; while, if 
through a short circuit or ground the current is kept 
on for any great length of time, the clockwork will 
open the circuit. 


CHAPTER VI. 


PRIMARY AND SECONDARY BATTERIES. 


The Figures 55 to 58 show different ways in which 
batteries may be grouped. Figure 55 shows the usual 
nanner. In this way the highest E. M. F. is ob- 




FIGURE 55. 




FIGURE 56. 


tained, and also the best results in all cases where the 
line resistance exceeds the battery resistance. It must 
be borne in mind that the battery has an internal re¬ 
sistance independent of that of the line, and this in- 


± 


FIGURE 57. 

ternal resistance will modify the current quite as much 
as any other resistance. The battery resistance varies 
inversely as the surface of the plates exposed in the 
liquid, and directly as their distance apart. 

Taking into consideration this law, we can readily 
see that six cells placed in multiple, as in Figure 56* 

66 
























PRIMARY BATTERIES 


67 


will have but one-fourth the resistance of those in 
Figure 55. In Figure 55 the resistance of six cells 

is 6 X R; in Figure 56 it is — ^ in Figure 57 it is 

£ 

--and in Figure 58 it is^ Also in any ar¬ 
rangement of cells the internal resistance of the bat- 

X X R 


tery equals 


N 


w r here X stands for the number 


of cells in series; R for the resistance of one cell and 
N for the number of groups in parallel. 



t=i ' r::~ — l— j ... i — 'T i 1 —- —nn — 

FIGURE 58. 


The total E. M. F. of any battery equals NXE, 
where N stands for the number of cells in series and 
E for the E. M. F. of one cell. The E. M. F. of any 
cell is independent of its size, and while no current is 
flowing is independent of its internal resistance. When 
current is flowing, however, the drop in E. M. F. is 
equal to the current X the internal resistance. As 
the internal resistance of all primary cells is quite 
high, this fact must not be overlooked whenever large 
currents are to be used. 

As a general rule cells should be so grouped that 
their internal resistance is nearest equal to that of 

















68 


WIRING DIAGRAMS 


the line and instruments through which they are to 
work. 

Where very high resistance lines are worked, as in 
telegraphy, for instance, the internal resistance of the 
battery is of little consequence, since an addition of 
100 ohms resistance to a circuit of several thousand 
ohms would hardly be noticeable. For circuits of low 
resistance, such as gas lighting, it is, however, an 
item which must not be overlooked. The resistance 
of an average gas lighting circuit does not exceed a 
few ohms, and to place into such a circuit a battery 
having ten or twenty ohms resistance would obviously 
be poor practice. Where large currents are used it 
is advisable to use large cells. Placing small cells in 
multiple has many disadvantages, and great care must 
be taken that all cells are of the same E. M. F., and 
they should also be of the same make. 

There are two general classes of primary batteries, 
each suited to a different class of work. 

For all intermittent work an open circuit battery 
should be chosen. Cells of this kind will last a very 
long time on open circuit without deterioration, but 
must never be left on short circuit or used for continu¬ 
ous work. 

Perhaps the best known of all open circuit batteries 
is the Leclanche cell, and the instructions here given 
will apply most specifically to it, but can be followed 
in general with all open circuit cells. 


PRIMARY BATTERIES 


69 


Never use more sal ammoniac than will be readily 
dissolved; about six ounces will be sufficient for ordi¬ 
nary use. It is preferable to make a saturated solu¬ 
tion of sal ammoniac, and after filtering it through 
cloth or cotton wool, add about 10 per cent, of water. 

Do not fill jars more than three-fourths full of so¬ 
lution, and keep them in a cool place, well inclosed, to 
prevent evaporation. 

Never allow your battery to freeze. 

Keep all exposed parts covered with paraffine and 
see that all connections are clean and tight. 

Do not allow the battery to be short-circuited or 
run down. If this has occurred let it remain on open 
circuit for a few hours; it will often pick up. 

If the solution appears milky it is an indication 

* 

that more sal ammoniac is required. It will also be 
beneficial to remove the carbon and let it dry out 
thoroughly before using again. 

Impure zincs which do not eat away evenly facili¬ 
tate the formation of crystals, which greatly increase 
the resistance, and if not removed will destroy the 
action of the battery. 

Dry batteries for general use are made up of the 
same materials as open circuit batteries, the main 
difference being that the material is applied in the 
form of a paste. They are used quite extensively 
for portable work. When run down some of them 
may be recharged by sending a current of two or 
three amperes through them for a few hours. 



70 


WIRING DIAGRAMS 


If they are dried out so that current will not flow 
through them an opening may be made in the shell 
and the cell then soaked in a solution of sal ammoniac. 
This will facilitate charging. The opening should 
be sealed again to prevent evaporation. As the shells 
of the cells usually consist of the zinc element, it is 
well to see that they are covered, or at least that two 
cells do not touch. 

The primary battery commonly used for closed cir¬ 
cuit work, or continuous work, is the so-called “crow¬ 
foot” or gravity battery. The copper element rests on 
the bottom of the glass jar. The jar is filled w r ith 
clean water and enough sulphate of copper (blue 
vitriol) is added to give a blue tint to about one-half 
of the water. The blue line should be maintained 
about midway between the copper and the zinc, which 
is suspended from the top of the jar, and is usually 
made in the shape of a crow’s foot. 

When this battery is first set up it should be short- 
circuited for several hours, and it must be kept in 
action, as it deteriorates rapidly when left on open 
circuit. 

While this battery remains in action the specific 
gravity of the upper solution increases. This solu¬ 
tion should be maintained at about 25 degrees hy¬ 
drometer test. If it falls below this the battery should 
be short-circuited for a little while. If it goes be¬ 
yond this, some of the solution must be removed and 
the rest diluted with clear w^ater. The resistance is 


SECONDARY BATTERIES 


71 


much increased by dense sulphate of zinc solution 
The zinc oxide which sometimes forms on the zinG 
may be removed with a brush and water. 

The gravity cell has a high internal resistance, 
and is suitable only where a continuous current flow 
of small quantity is desired. This cell and also the 
Leclanche exist in many modified forms. Enough 
has been said to enable anyone to select a suitable 
battery, and detailed instructions will be found with 
all batteries where such instructions are necessary. 

SECONDARY BATTERIES. 

Storage, or secondary batteries, as they are often 
called, are quite extensively used in latter day prac¬ 
tice. It is beyond the scope of this treatise to give 
anything but a few working directions covering gen¬ 
eral operation. Detailed instructions applicable to 
the different types will accompany most cells when 
purchased. 

The E. M. F. of secondary batteries will average 
a little over 2 volts. On discharging, the E. M. F. 
should not be allowed to fall below 1.8 volts. 

The charging should proceed slowly, and should 
never be carried beyond 2.5 volts. 

The charging E. M. F. should not exceed that of 
the battery more than 5 per cent. 

Cells should not be discharged more than two- 
thirds of their capacity. They should never stand 
uncharged. 


72 


WIRING DIAGRAMS 


In battery rooms all exposed metal work should 
be painted as a protection against acid fumes. 

Wooden floors should also be protected against 
acid. 

If charging is continued after the active material 
has been used up, oxygen and hydrogen gas will be 
given off. 

Pure sulphuric acid should be used, and this should 
be diluted with distilled water. Pour the acid into 
the water slowly. Never pour w^ater into acid, as 
much heat is generated. 

Whenever necessary, replenish evaporation with 
distilled water and mix well, as otherwise the water 
will float on top. 

Two methods of Measuring the internal resistance 
of batteries are shown in Figures 59 and 60. In 
Figure 59 A represents an ammeter and V a volt¬ 
meter. Instruments for this purpose must be chosen 
suitable to measure the small currents and E. M. F. 
likely to be used, and must have a scale sufficiently 
large to admit of reading fractions of volts and am¬ 
peres. To make the test, first close the circuit through 
the voltmeter. This gives us the E. M. F. of the 
whole battery, and may be called E. Next close the 
circuit through the ammeter and note the current 
reading; also at the same time note the reduced read¬ 
ing of the voltmeter and call this E'. The internal 

p_ -p / 

resistance of the battery is equal to-——- where A 



SECONDARY BATTERIES 


73 


is the number of amperes flowing through the am¬ 
meter, and the other two symbols as above. The 
readings must be taken in a very short time, or polar¬ 
ization will modify both current and voltage. If the 
ammeter used above is of very low resistance, an ad¬ 
ditional resistance should be placed in circuit with it 
to prevent excessive current flow. 



FIGURE 59. 



FIGURE 60. 


In Figure 60 no ammeter is needed, but the resist¬ 
ance of R must be known. Take the voltmeter read¬ 
ing as in Figure 59 and call it E. Next take the 
voltmeter reading with current flowing through R 
and call it EC The internal resistance of the battery 

E—E r 

is EC In other words, divide E r by R, which ghes 

IT 

the current flowing through R; then divide the dif¬ 
ference between E and E' by this current. The re¬ 
sult will be the battery resistance. 









































74 


WIRING DIAGRAMS 


A comparative test as to the value of the different 
batteries may be made in the following manner: Pro¬ 
cure the same number of cells of each kind to be test¬ 
ed. A suitable resistance and a voltmeter with a suita¬ 
ble scale must also be procured, and connections made 
as in Figure 60. The voltmeter should be of quite 
high resistance, so the current flowing through it 
will not materially affect the battery. The resistance 
should be about equal to the battery resistance. This 
will allow a current to flow which will gradually 
polarize any open circuit battery. When all is ready, 
close the circuit through R, and at regular intervals, 
of say one minute, note the fall in E. M. F. on the 
voltmeter until the battery is nearly polarized. Now 
open R and in the same way take readings at regular 
intervals, until the battery regains its former E. M. 
F.; or, if this is too long, for any convenient time. 

The figures obtained may be plotted in curves, as 
shown in Figure 61, where the time is plotted hori¬ 
zontally each division representing one minute, while 
the drop in E. M. F. is plotted vertically, two divi¬ 
sions representing one-tenth of one volt. 

The figure shows the polarization and recovery 
curves of a Laclede cell having an initial E. M. F. 
of 1.2 volts, and discharging through a resistance of 
3 ohms. During the first minute the E. M. F. fell 
to .78; during the second to .68; third to .62; fourth 
to .58; fifth to .55; and at the end of twenty-six min¬ 
utes it had fallen to .3. 


SECONDARY BATTERIES 


zo- 

Upon opening the circuit the E. M. F. rose during 
the first minute to .47, and during the second to .5; 
and then in a more gradual and steady manner as in¬ 
dicated by the curve. 



If all batteries are tested with the same resistance 
and voltmeter, and given the same time, the result 
must be fairly comparatn e. 





























































































































CHAPTER VII. 


CONNECTING UP-LOCATING TROUBLE. 

Figure 62 shows the rough wiring used to connect 
an annunciator with a call from each of the floors 
1, 2, 3, 4, and also a call from the office to each of 
those floors. This figure is introduced to illustrate a 



method of testing to find the proper wires to make 
connections, and it will be assumed that all of the 
wires are concealed and all are of the same color, so 
that it is impossible to trace out any part of the 

76 








































CONNECTING UP 


77 


wiring. Let it also be assumed that the party who is 
to connect the system did not install the wiring, and 
knows nothing about any part except the purpose for 
which it is installed. 

The first step should be to separate the wires at 
all outlets so there may be no accidental connec¬ 
tions which would cause confusion. The next step 
is to connect the battery to the two battery wires 
as shown, which will very likely be found without any 
trouble. Now go to floor 1 and bunch all wires 
found there, testing each wire to all other wires with 
a portable bell before connecting. If a ring is ob¬ 
tained it is an indication of a short circuit or wrong 
connection, which must be located and corrected be¬ 
fore proceeding farther. Next proceed to the push 
buttons, P, and with the test bell find the wire com¬ 
ing from 1 ; when the bell is connected to the wire 
coming from 1 and to the battery wire a ring will be 
obtained. Now take up the annunciator wires and 
find the wire coming from 1 in the same way. 

Having now found one wire which rings with two 
others, this must be the battery wire, and may be 
connected to one side of all the pushes, and to the 
annunciator through the bell. The other two wires 
may be marked and the connections at 1 removed. 
After this has been done, connect the two wires com¬ 
ing from 1 each to its proper place, push 1, and drop 
1 "respectively, and fix the push button so it will 
keep the circuit closed. Had this been done without 


78 


WIRING DIAGRAMS 


first opening the connections on floor 1, a short-cir¬ 
cuit would have been the result. 

Now return to 1 and find the wire which rings the 
annunciator, and also the one which rings the test 
bell without disturbing the annunciator. The one 
wire used in common for both is the battery w r ire, 
and connects to one side of the bell and also to the 
push for annunciator. The wire leading to push P 
is to go on the other side of bell, while the one lead¬ 
ing to annunciator goes to the other side of push 
button.. The fourth wire must necessarily be the 
battery wire leading to the floor above, and is to 
be connected to battery wire coming from floor be¬ 
low. 

Por these tests a bell to act either single stroke or 
vibrating is very useful, especially when the annun¬ 
ciator is so far away that the ringing of its bells 
cannot be heard. A bell of this kind will indicate 
at once whether the wire through which it rings is 
connected with the annunciator or the push buttons, 
since it w r ill ring vibrating in series with the annun¬ 
ciator bell and single stroke in connection w T ith the 
push button wire. 

The foregoing tests represent a great deal of 
time and labor, much of which may be avoided by 
using w r ire of one color for the battery wire and a 
different color for all the other wdres on each floor. 
For Figure 62 this would require five colors. With 
wires arranged this way, the steps necessary to con- 


LOCATING TROUBLE 


79 


nect up the system will be: First connect the bat¬ 
tery wires on the different floors so that there will 
be one continuous wire from the battery to the fourth 
floor. While doing this note the color of wire used 
on each floor, so that the annunciator and push but¬ 
ton wires may be connected up accordingly. After 
connecting these and the battery, return to each 
floor and set up the bell and connect it to the bat¬ 
tery wire. Now touch one of the two remaining 
wires to the bell; if it rings it is the wire coming 
from the annunciator, and the other is the proper 
wire to connect to the bell. 

Always locate the battery as near as possible to 
the push buttons. In this way the chance of leakage 
may be reduced to a minimum, since one wire only 
is exposed for any considerable length, the other be¬ 
ing cut short by the pushes. 

When one is alone a bell and battery is a very 
valuable help in fish work. Insert one piece of wire 
coming from the battery into the ceiling where it 
is expected to bring the wire to. Connect the fish 
wire to the other side of the battery and proceed in 
the usual way. When the two wires meet the bell 
will ring. 

LOCATING TROUBLE. 

While looking for trouble always work according to 
a fixed plan; haphazard testing and guessing will 
usually waste time. In all cases the most important 
thing to ascertain is whether the battery is in work- 



80 


WIRING DIAGRAMS 


mg order. If there are several bells and any one 
of them is working properly, the battery may be set 
down as all right. If there is no bell in operation, 
and none at hand, the most convenient way to test 
the battery is by “tasting”; arrange wires so that 
both poles come in contact with your tongue, if 
the battery is in order you will notice a peculiar taste, 
and a little experience will enable anyone to deter¬ 
mine, approximately, whether the current is in pro¬ 
portion to the number of cells employed. 

It will be well to avoid “tasting” circuits provided 
with an unusual number of cells and large magnets 
or spark coils, as the taste is apt to be very strong, 
especially if the wires are allowed to meet on the 
tongue and then break. If no current is obtained 
at the battery, examine the binding posts and con¬ 
nections; see whether each jar is properly filled and 
whether any of the zincs have been eaten away, or 
covered with crystals, which often causes a total ces¬ 
sation of current. If the battery is not found de¬ 
fective in any of the above points it may be entirely 
run down, either from overwork or a short circuit. 

Some idea of the trouble may often be gained by 
questioning parties interested. If the bells stop 
suddenly it would indicate a broken line or a short 
circuit. If any bell were ringing continuously tor a 
long time it would run the battery down. If the bat¬ 
tery has been merely run down it will pick up in a 
short time if left on open circuit. A small galvano- 


LOCATING TROUBLE 


81 


meter is very useful and will soon indicate whether 
a battery is picking up; it may also be used to test 
each cell separately. In any case, it is best to have 
the battery in good working order before looking 
elsewhere for the cause of trouble. If the battery is 
in order the next step (if there is but one bell) should 
be to examine the bell and push buttons; see that 
contact points are in order and that the bell is prop¬ 
erly adjusted; also examine the line connections and 
see that they are clean and tight. A portable bat¬ 
tery is very convenient, and with it one can quickly 
determine whether the bell is in order. 

If, after the foregoing, the bell still fails to work, 
the trouble must be looked for in the line, and it 
will be well to examine the wires near bell and push 
buttons, as these wires are handled quite often for 
various reasons, and will often be found broken quite 
close to their connections. Splices are also quite often 
to be found quite close to terminals, as wires are often 
cut short when installed. When there are several bells 
and all fail to work, the inference would naturally be 
that the main battery wires are either broken or short 
circuited. If the battery is in good working order, 
one may be certain that no short circuit exists, and 
an open circuit must therefore be looked for. 

From the many foregoing diagrams it will be seen 
that in all ordinary multiple bell systems, one wire 
coming from the battery leads to the bells and the 
other to the uush buttons; this does not mean that 


82 


WIRING DIAGRAMS 


the bells must all connect to the same wire and the 
push buttons to the other, since, in Figure 63, the 
location of any bell and its push button might be 
exchanged without hindering its operation. In Fig¬ 
ure 63, 1 and 2 are the battery wires connecting with 
bells and buttons as shown. Suppose none of the 
bells will ring and we have come to the conclusion 
that one of the battery wires is broken; the best way 
to locate a break in the main wires is with a test bell, 
starting from the battery end of the line. At any 



convenient place where both battery wires are access¬ 
ible, say at A and B, connect the test bell; a ring 
will show that the line between it and battery is in 
order, while failure to ring would indicate the break 
to be between it and the battery. Suppose no ring 
has been obtained and we now wish to ascertain which 
one of the main wires is broken; we can do so by 
running a temporary wire from B back to the bat¬ 
tery as shown by the dotted lines. If the wire (i) 
is not broken between B and the battery, a ring will 
be obtained when connections are made to the oppo¬ 
site battery pole. If the wire is broken no ring can 


























LOCATING TROUBLE 


83 


be had from either battery pole; but when the teim 
porary wire is connected to the wire and pole of the 
battery in which the break is, the whole system will 
be in working order. 

If a short circuit exists, say at C and D, Figure 
64, one way to locate it is by cutting a bell into the 
circuit at the battery. If the battery has been run 
down by the “short,” as will likely be, one must either 
recharge or wait for it to pick up, unless an extra 
battery is at hand. Having connected the bell near 



FIGURE 64. 


the battery, we can now cut one of the main wires 
at any available place. If this stops the bell ring¬ 
ing, the short circuit is farther from the battery; if 
it does not stop the bell the short circuit is between 
the cut and the bell. If a portable battery is at 
hand, it and the bell may be carried about and cut 
into the circuit wherever desired. In this case the 
regular battery should be disconnected and the bat¬ 
tery wires connected together. If the short circuit 
exists at C and D, as aforesaid, and the battery is 
cut in at X, a ring will be obtained; while when we 
get beyond the short circuit and cut in at Y, no ring 






























84 


WIRING DIAGRAMS 


can be obtained. By making several tests as out¬ 
lined above, the seat of trouble can be very closely 
located. The foregoing instructions assume that the 
wiring is concealed or that a close inspection is very 
difficult. Short circuits will generally be found 
where wires cross metal pipes or bars, or where one 
staple holds two or more wires. Wire lath is also 
a very prolific cause of short circuits, and it must be 
borne in mind that two grounds on opposite wires 
are equal to a short circuit. As a matter of fact if 
a bell system can be kept clear of grounds, there will 
be but very little trouble from short circuits. 

An easy and also a sufficient test for battery bell 
systems can be made by means of a strong magneto. 
Connect the magneto in place of the battery and 
give it a few sharp turns; if a ring is obtained the 
insulation between opposite poles is weak. This may 
be caused by the leak across the surface of a push 
button or kindred device, or it may be the result of 
poor general insulation, both poles being slightly 
grounded. A ground on one side only would not 
be discovered in the above test. 

To test the insulation resistance to ground, con¬ 
nect one wire of the magneto to a convenient water 
or gas pipe, the former being preferred on account 
of the poor conductivity often caused by rust or 
red lead in the joints of the gas pipes; the other 
wire connects to the whole bell system without the 
battery. If, on turning the magneto, a ring is ob~ 


LOCATING TROUBLE 


85 


tained, it is an indication of poor insulation resist¬ 
ance, and very likely some of the wiring is located in 
a damp place or in contact with metal or other 
grounded material. By disconnecting one of the 
battery w T ires one can easily determine on which side 
of a system a ground may be located. All grounds 
should be removed, as they are the cause of leaks 
which run batteries down, and in time may cause a 
broken wire through electrolytic action. In tele¬ 
phone systems one or more grounds may also serious¬ 
ly interfere w r ith the talking qualities of a line, even 
if the grounds are all on one side of the circuit. 



CHAPTER VIII. 


MISCELLANEOUS. 

Whenever a current is flowing in a wire it pro¬ 
duces lines of force surrounding that wire. If the 
current in the wire flows away from the observer 
the lines of force will encircle the wire from left to 
right, i. e ., clockwise. (See Figure 65.) Lines of 
force always enter a magnet (compass needle) at 
the south seeking pole and leave it at the north seek¬ 
ing end. 


FIGURE 65. 

From this it follows that if a compass be held 
under a wire in which a current is flowing from you 
the north seeking end of the needle will deflect toward 
the left; while if the current is flowing toward you it 


N S 



will deflect toward the right. If the compass is held 
above the wire the deflections will be the reverse of 
the above, as shown in Figure 66. 

86 









MISCELLANEOUS 


87 


Unless an extremely delicate compass be at hand, 
this method of determining the directions of currents 
in wires wfill be confined to comparatively large cur¬ 
rents. If there are any magnets in the circuit, and 
if we know the direction in which they are wound, 
we can very easily determine the direction of the 
current, since the relative direction of current and 
magnetism will be as in Figure 67. 


FIGURE 67. 



If there is no magnet available, one may be tem¬ 
porarily constructed out of a screwdriver or pocket- 
knife by taking a few turns of the current carrying 
wire around it. If no compass is at hand, one can 
be made from a piece of cork and a steel needle set 
afloat in a cup of water, the needle being first mag¬ 
netized. 

If the right hand be held above a wire as in Fig¬ 
ure 67, in which the current is flowing from you and 
the winding as shown in the figure, the north pole of 









88 


WIRING DIAGRAMS 


the magnet will be as shown. If the direction of 
winding be reversed, or the direction of the current- 
the north pole will be at the other end. 

All magnets have a retarding effect on alternating 
or intermittent currents. With an arrangement as 
shown in Figure 68, a lightning discharge will gen¬ 
erally jump the small distance between the points of 
the lightning arrester rather than pass through the 




coils of the magnet. When, however, a current has 
once been started around a magnet it has a strong 
tendency to continue, and will manifest itself in a long 
spark if suddenly interrupted, as in a gas-lighting 
spark coil, for instance. Figure 69 is drawn to il¬ 
lustrate this, and the magnet there shown is of very 
low resistance compared with the lamp shown in mul¬ 
tiple with it. If the battery circuit is closed the mag¬ 
net will be energized, but no appreciable current will 
flow through the lamp. If now the battery circuit is 
Buddenly opened, there will be a strong current dis¬ 
charge through the lamp, causing it to flash up for 
an instant. 































MISCELLANEOUS 


89 


Figure 70 is designed to illustrate some of the dif¬ 
ferences in electrical currents. The winding of mag¬ 
net A, if properly proportioned, will be found to be 
almost impenetrable to rapidly alternating or inter¬ 
mittent currents, while it may offer hardly any re¬ 
sistance to continuous currents. A continuous cur- 








B 

- 



mu; 


3 


FIGURE 70. 


rent working an ordinary bell would be much retarded 
by it, however, and the bell would work very slow. 
B has two windings opposed to each other. If one 
winding only is in circuit it will act similar to A; if 



FIGURE 71. 


the switch on the second winding is closed there will 
be but little retardation. The condenser C entirely 
prevents the passage of continuous currents, but tele¬ 
phonic currents pass readily through, and polarized 
bells may also be made to ring through it. 

Figure 71 shows the plan of an ordinary induction 
coil. The iron core when energized attracts the in¬ 
terrupter, and this breaks the current at C, as in a 

























































90 


WIRING DIAGRAMS 


vibrating bell. At every make and break in the 
primary circuit secondary currents are induced in 
the fine secondary winding. The circuit breaker is 
bridged by a condenser in order to reduce the spark¬ 
ing to some extent. With cheap coils the condenser 
is usually omitted. 

Two wires carrying current in the same direction 
will attract each other, while if currents are in oppo¬ 
site directions they will repel each other. 

A leak to ground on a positive wire will gradually 
destroy it; the negative will not be affected much. 

An easy method of determining the direction of 
current consists in letting the current pass through a 
little water confined in a cup. The current will flow 
from the positive pole to the wire at which small 
hydrogen bubbles appear, which is the negative. 
This method is not applicable to low voltage systems. 

The contacts of bells, relays and other devices 
which produce frequent interruptions in current, 
should consist of platinum. To determine whether 
they are platinum or not, drop a little nitric acid 
on them; this acid will not affect platinum, but will 
attack German silver and other imitations. 

A continuous current will carry an arc much longer 
than an alternating current. It also produces a 
chemical action directly in proportion to its amount 
in amperes. 

A magnet in an alternating circuit will greatly re¬ 
duce the current, and the iron will be heated by the 


MISCELLANEOUS 


91 


frequent reversals in the direction of magnetism. If 
the magnet is large and the frequency of the alter¬ 
nations is very great, only a very small amount of 
current will flow. The magnetism has no such effect 
on continuous currents. The heat generated in a 
continuous current magnet is produced by the re¬ 
sistance in the wire only, and the current flow de¬ 
pends on this resistance only. Alternating currents 
are also greatly retarded and diminished by lead cov¬ 
ered wire or wires run in iron pipe. These wires act 
as condensers and currents are also induced in them. 
Whenever it is necessary to run wires in this way, 
both wires should be enclosed in the same sheath or 
pipe. Continuous currents are not affected in this 
way except for an instant at make or break. 


USEFUL FACTS AND FORMULAS. 


In any direct current circuit the current equals the 


electromotive force divided by the resistance, I = 


E 

R- 


One application of this law is indicated in Figure 
72, where the voltmeter V is used to measure cur¬ 
rent. The value of R being known, the current flow¬ 
ing through R is equal to the voltmeter reading, E, 
divided by R, the resistance. 

E 

From the formula I = —— two others are deduced. 


In Figure 73, knowing the value of the electromotive 




G2 


WIRING DIAGRAMS 


force E, and current I, we can find the resistance R 

E 

by dividing E by I, R =-y-. Knowing the current 

I end the resistance R, we can find the electromotive 
force E, by multiplying I with R, E = IR. 

The volts lost in any circuit equal the resistance 
of that circuit multiplied by the current. 


C 



FIGURE 72. FIGURE 73. 


Currents of electricity divide among derived cir¬ 
cuits in proportion to their conductivities, which is the 
inverse ratio of their resistances; i. e., the lower re¬ 
sistance takes the most current. The joint resist¬ 
ance of two circuits in parallel is equal to the product 
of the two resistances divided by their sum. 

In Figure 74 - f - * = %y 2 . 

O “T* O 

The joint resistance of any number of circuits in 
parallel if all are equal, may be found by dividing 
the resistance of one circuit by the total number of 
circuits. The joint resistance of any number of cir- 

























MISCELLANEOUS 


93 


cuits in parallel, whether they are equal or not, is 
the reciprocal of the sum of the reciprocals of their 
resistances. Joint resistance equals 

1 

L _L _L 

R + R' + R" 

where R, R', R", are different resistances. The re¬ 
ciprocal of a number is 1 divided by that number, 
thus one-tenth is the reciprocal of 10. 



To find the total current. Figure 75, we must first 
find the joint resistance of 20 and 30, which, accord¬ 
ing to the above formula, is 12. Next add this to 
the other resistance 10, in the circuit, and divide the 
electromotive force 11, by this sum. The result is 
one-half ampere, of which three-tenths will pass 
through B and two-tenths through C. 

The multiplying power of a shunt is the ratio of 
the total current flowing in the circuit to that part 
of it which flows through the ammeter. The shunt 





















94 


WIRING DIAGRAMS 


required to give a certain multiplying power is found 
by dividing the resistance to be shunted by the mul¬ 
tiplying power desired minus 1. Thus, if the mul¬ 
tiplying power desired is ten, we divide by 10 — 1, 
which is 9. If the resistance to be shunted is 100 
ohms, the proper resistance of the shunt is 100 di¬ 
vided by 9, which is 11 1/9 ohms. Nine-tenths of 
the current will flow through this shunt and 1/10 
will flow through the ammeter. 

The amount of work done by a current of elec¬ 
tricity is measured in watts. To determine the num¬ 
ber of watts multiply the square of the current by the 
resistance, or W = I 2 R. For instance, the heat gen¬ 
erated in a wire is proportional to the square of the 
current; thus, doubling the current will produce four 
times as much heat. Other formulas for determin¬ 
ing the watts deduced from the above, using Ohm’s 
law, are: W=I E, or the current times the electromo¬ 
tive force, W = E 2 /R, or watts equals the electro¬ 
motive force squared divided by the resistance. One 
horse-pow r er equals 746 watts. To reduce to horse¬ 
power divide the w r atts by 746. 

The magnetism produced in an iron core is to a 
certain extent proportional to the number of ampere 
turns (current times the number of turns of wire) 
but when the point of saturation is reached, although 
the magnetizing force is increased, still there will be 
but little increase in magnetism. Figure 76 illus¬ 
trates the increase in magnetism in w ? rought iron and 


MISCELLANEOUS 


95 


cast iron, the magnetizing force (ampere turns) be¬ 
ing represented by the distance measured along the 
horizontal line and the resulting magnetism by the 
distance along the vertical line. This is important 
to bear in mind when adjusting field coils or rheostats 
on dynamos or motors. 

The circumference of a circle is found by multi¬ 
plying the diameter by 3.1416, or roughly 3 1/7. 

The area of a circle is found by multiplying the 
square of the diameter by .7854, or the square of 
the radius by 3.1416. 



The circular mils in a wire may be found by mul¬ 
tiplying the diameter in mils (1000 mils per inch) 
by itself. 

To convert circular mils into square mils multiply 

by .7854. . # 

To convert square mils into circular mils divide by 

.7854. 

„ . . d 2 

The weight per mile of pure copper wire is ^5 

where d is given in mils. 










































96 


WIRING DIAGRAMS 


The resistance of copper wire increases 21/100 of 
1 / for each degree rise in Fahrenheit. 

The resistance per mile of pure copper wire is 


, , 54882 j . . . 

about ■——, d being in mils. 


d ? 

The weight of iron wire per mile is — where d is 

/ AJ 


the diameter in mils. 

The resistance per mile of galvanized iron wire is 
about ? d being in mils; or about seven times 


that of copper. 

The resistance of German silver is about thirteen 
times that of copper. 




CHAPTER IX. 


ELECTRIC LIGHTING. 

Figure 77 shows what is known as the tree system 
of electric light distribution. The wires at the lowest 
floor must be of sufficient capacity to carry the total 
current. At each floor or succeeding center of dis¬ 
tribution the size of mains may be reduced, suitable 



FIGURE 77. FIGURE 78. FIGURE 79. 


cutouts being provided as shown in the diagram. 
This system is not to be recommended, as it will 
result in great difference of potential between those 
branch circuits nearest the dynamo and those at the 

97 




































































































































































98 


WIRING DIAGRAMS 


extreme end of the system. When the mains are fully 
loaded, the nearest lamps will either burn too bright 
or those at a greater distance be dim. 

This difficulty is largely overcome by the arrange¬ 
ment shown in Figure 78. 

Figure 79 shows a system of distribution which is 
very often used. The mains are run direct from the 
dynamo, or street service, to the last center of dis¬ 
tribution without changing size of wire. While this 
system has some of the disadvantages of the tree 
system in regard to drop, still the losses are greatly 
reduced owing to the much smaller losses on the 
mains between those centers farthest away from the 
source of supply. If the mains are of small size they 
may be run directly through the branch blocks at 
the various centers, as shown at the upper part of the 
figure. If the mains are too large to be run directly 
through the blocks, either of the methods shown in 
the lower part of the figure may be used, that shown 
at the bottom being preferable for, in case of a short 
circuit, across the contacts on the branch blocks, the 
smaller fuse will blow, while if the method shown in 
the center is used the main fuse will blow. This ar¬ 
rangement also allows any center to be disconnected for 
testing without affecting the remainder of the circuits. 

Figure 79a shows how a two wire system may be 
converted into a three wire. One extra wire will have 
to be run. If the change over results in doubling the 
voltage of the system this wire will not require to be 


ELECTRIC LIGHTING 


99 

as large as the original wires and should be connected 
to the neutral i. e. should run to all of the cutouts as 
shown in cut. 



FIGURE 79a. FIGURE 79b. FIGURE 79c. 


Figure 79b shows method of arranging cutouts so 
that all branch wires on any side of box are of the same 
polarity. This is frequently of use in electric signs 
where large numbers of wires are often bunched. 

In Figure 79c a three wire system is shown converted 
into a two wire. As this usually is accompanied by a 



FIGURE 79d. 


reduction in voltage and a consequent increase in 
current for the same number of lights it will likely be 
necessary to run an additional wire and divide the 
cutouts as shown. 

















































































































100 


WIRING DIAGRAMS 


Figure 79d shows the manner of connecting cutouts 
to a three phase system where cutouts are scattered 
along the line. Particular attention must be given to 
see that lights are as near as possible balanced between 
the phases. 



FIGURE 79e. 



The delta connection for cutouts grouped together 
is given in Figure 79e. By tracing out the diagram it 
can readily be seen that the cutout connections are 
similar to the connections of the single lamps shown 
at the right. 



FIGURE 79f. 



The voltage of lamps used in connection with this 
arrangement must be the same as that of the phases. 
The star connection of cutouts is given in Figure 

































































ELECTRIC LIGHTING 


101 


79f. If this connection is used it should have a balanc¬ 
ing wire as shown. 

The voltage of lamps to be used in connection with 
this system must be equal to the voltage of the phases 
divided by 1.73. This method is not generally used. 


S 






FIGURE 80. 


6 0 

0 O 


Figure 80 shows a two-wire circuit with seven 
lights controlled by a double-pole switch, S; three 
lights controlled by a single-pole switch. S'; and two 
lights not controlled by any switch. 

ooooooo 0-£> 

>;o o o o o o o o o 

FIGURE 81. 

Figures 81 and 82 show three-wire circuits. Fig¬ 
ure 81 is arranged with double-pole switches, each 
switch completely disconnecting the wires controlled 
by it. In Figure 82 only the two outside wires are 
broken, the neutral wire remaining intact. When 
single-pole switches are used in connection with three- 
wire systems, they should be placed on one of the 
outside wires, as the neutral wire is nearly always 





























102 


WIRING DIAGRAMS 


grounded. No switch must ever be connected so as 
to make it possible to break the neutral wire without 
also breaking the outside wires at the same instant. 

0 Q Q Q Q ~\ 


Ol 



-o- 

■K ---<! 

o 

O 

O 

o 

o 

Q 



- m—r r-+ 

DOOOOOOOOOOO 


FIGURE 82. 


Figure 83 shows a double-pole method of control¬ 
ling a circuit from two places. 





:Q 


o 


*' * ° 



FIGURE 83. 


In Figure 84 a similar arrangement is shown act¬ 
ing single-pole and arranged at one end for a throw- 
over knife switch and at the other for a three-way 
snap switch. 


A A 


■ -i 





_ 





l 



Figure 84. 


By Figure 85 the same-result is accomplished, and 
in some cases this method may be more saving of wire 
than Figure 84; but it cannot be used in connection 
with direct-current arc larnpSj as the polarity may be 
reversed in turning lamps Ah and off. 










































ELECTRIC LIGHTING 


103 


Figure 86 shows a method of controlling a circuit 
from any number of stations. Any number of double¬ 
pole switches, as shown in the center, may be cut into 



the line. Snap switches as shown in Figure 87 may 
also be used in place of the throw-over knife switch. 



FIGURE 86. 


By the system shown in Figure 87, a circuit can 
also be controlled from any number ot places. The 
single-pole switches remain in the center and other 



FIGURE 87. 


switches are added as required. With this arrange¬ 
ment polarities may also be reversed in turning lamps 

on and off. 


















































104 


WIRING DIAGRAMS 


Figure 88 is known as an equal potential loop. 
This is useful on long lines where there is consider¬ 
able loss; all lamps receive the same pressure and burn 
at the same candle-power. 



0.. 0 0 .0... 0 Q 

FIGURE 88. 



Figure 89 shows a method by which lamps may be 
used at full candle-power; or, by throwing the 
switch over, they may be used at half candle-power^ 
two in series. 



FIGURE 89. 


Figure 90 shows one switch arranged to burn 
either two, four or six lamps. When connected at 1, 
the two top lights alone will burn; at 2 the four bot- 




O 


FIGURE 90. 


tom lights will burn alone, while by connecting 2 and 
3 all six lights will burn. 





























ELECTRIC LIGHTING 


105 


Figure 91 shows wiring arranged to provide a guest 
call for hotels or similar places. The bell 2 will ring 
and the lamp in series with it will burn only as long 
as the switch at the cutout remains closed. If the 
double-throw switch is thrown over, the bell 1 will 



continue to ring and the lamp will burn until the 
guest throws his switch over, or the party calling re¬ 
turns his to the original position. 



In Figure 92 the wiring for low-tension arc lamps 
is shown. Such lamps may be wired either in series 
or in multiple, the wiring being arranged to suit the 
kind of lamps used. With all lamps of this kind 
some resistance must be used. With lamps run in 

































































106 


WIRING DIAGRAMS 


multiple it is usually provided with each lamp, and 
is generally built in with the lamp. 

Figure 93 shows a throw-over switch so arranged 
that only one lamp at a time can be used, one resist¬ 
ance answering for both. All switches used in con¬ 



nection with direct-current arc lamps must be ar¬ 
ranged so that polarities cannot be changed by them. 

Figure 94 shows connections enabling one to burn 
either the two lamps at the right or those at the left, 
only two at a time being used. This arrangement re¬ 
quires the use of series lamps. 



FIGURE 94. 


Figure 95 shows a system of wiring which makes 
it possible to light all of the lamps in a building, 
not controlled by key sockets, from three different 
places at any time, even after they have been turned 

















































ELECTRIC LIGHTING 


107 


off by the occupants of rooms. In the top part of 
the figure one double-throw switch and one three-way 



FIGURE 95. 

snap switch are shown. Whenever, by either of 
these switches, the lamps are turned off, the switches 





































































































108 


WIRING DIAGRAMS 


make connection with the cutouts above, so that by 
throwing any one of the three knife-switches the 
lamps may be lighted again. In the lower part of 
the figure one circuit is arranged for the same pur¬ 
pose. By closing the single-pole swdtch S, all of the 
lights may be turned on at any time, excepting, of 
course, those that are turned off at the sockets. This 
arrangement is very useful in case of fire, or any 
emergency where it is desired to illuminate a whole 
house quickly. 



i 

O O 

o- 

o- 

o- 

o- 

V * 

z 

o o 

~s~ 

1 + 

t~™i 

?-s- 

9 9 9 

rtf ft 

-o 

--o 


FIGURE 96. 


Figure 96 shows the wiring of a convertible system. 
By means of the three-wire switch, connections may 
be made to either a two or three-wire supplv. With 
this system the middle or neutral wire should have 
as much carrying capacity as both outside -wires, since 
when used with a two-wire supply it must carry the 
full load, while either of the outside wires need carry 
but half the current. Cutouts of the kind shown in 
group 1 should not be used in connection with this 
system. They are not very objectionable in straight 
three-wire systems, but when used in connection with 
two-wire systems the middle fuse must be doubled to 








































ELECTRIC LIGHTING 


109 


carry the load. Such cutouts as are shown in group 
2 are preferable. Great care is necessary when arc 
lamps are to be connected to such a system. They 
can be connected with one side of the neutral only, 
and this side must be arranged so that polarities are 
not reversed when the main switch is thrown over. 



FIGURE 97. 



Where arc lamps are used extensively and where it is 
necessary to balance the load, as on the Edison three- 
wire system, the wiring used in Fig. 9< may be em¬ 
ployed. In place of the two double-pole, double¬ 
throw switches, a four-pole, double-throw switch may 

be used. 


FEED 


2 =&- 



nrr'TTD QS 


Figure 98 shows incandescent lamps arranged in 
series. This plan of lighting is generally used in 
connection with street railway work. The figure 
shows 550 volt circuits provided with lamps of differ- 




















































110 


WIRING DIAGRAMS 


ent voltage. Instead of the ground a return wire 
may be used. 

Figure 99 shows the wiring of a high-tension arc 
circuit. A group of incandescent lamps is also 
shown. When incandescent lamps are used in con¬ 
nection with arc lamps as shown there must be 
enough lamps in each group to take the current used 
by the arc lamps. The switch S controls the incan¬ 
descent lamps and also the arc lamps 1, 2, S by 
simply short-circuiting them. The double-pole switch 



FIGURE 99. 


S' controls the group A and is so arranged that when 
turned off this group is entirely disconnected. This 
is the only safe way of switching high-tension arcs: 
where they are merely short-circuited they are nearly 
as unsafe to handle as when burning. At B one 
incandescent lamp is shown controlled by a single-pole 
switch. When this lamp is burning it robs the arc 
lamp of as much current as it requires, the amount 
of current depending on the candle-power of the 





























ELECTRIC LIGHTING 


111 


lamp. Incandescent lamps should be used on arc cir¬ 
cuits only in an emergency and then only where there 
is little risk of fire. 

Figure 100 shows a diagram of the connections of 
a theater switchboard. The board is fed by the two 
sets of mains shown by the arrows on the lower sets 
of bus bars. The lower set of bus bars feeds the 
lights in the house, or auditorium, switch 51 control¬ 
ling the majority of these lights. A set of bus bars 
running from this switch feeds a number of smaller 
main switches which control all the lights in the differ¬ 
ent sections of the house, such as the gallery, bal¬ 
cony, main floor, etc. Bus bars running from these 
switches feed other switches which control the differ¬ 
ent groups of lights in the various sections of the 
house. 

The other set of main bus bars at the bottom of 
the board feeds the lights on the stage, these lights 
being controlled by four main switches: 24, which 
controls all the white lights; 35, all the red lights, 
and 43, all the blue lights, smaller switches being used 
to control the different colored lights in the foots, 
borders, strips, etc. 

The switches which operate the white lights, 17 to 
23 and 26 to 32, are all double-throw, the upper con¬ 
tacts of which are connected to a set of bus bars con¬ 
trolled by the main white switch, 24, while the lower 
contacts are connected to a set of bus bars indepen¬ 
dent of this switch. By means of this arrangement 


112 


WIRING DIAGRAMS 


part of the lights can be thrown off by the main 
switch while certain ones are left burning. 



H I House Bus Bar 

FIGURE 100. 


A few of the circuits are shown connected to the 
dimmers from which they run to the branch circuit 
cutouts. 




































































































































































































ELECTRIC LIGHTING 


m 


1 . 

White Strips. 

37. 

Red Border, No. 1. 

2. 

Red Strips. 

38. 

Red Border, No. 2. 

3. 

Blue Strips. 

39. 

Red Border, No. 3. 

4. 

Switchboard Lights. (Con¬ 

40. 

Red Border, No. 4. 


nected to House Bus 

41. 

Red Border, No. 5. 


Bar.) 

42. 

Red Proscenium. 

5. 

Sub-basement Lights. 

43. 

Blue Main. 

6. 

Basement Lights. 

44. 

Blue Foots. 

7. 

Basement Lights. 

45. 

Blue Border, No. 1. 

8 . 

Paint Bridge Motor. 

46. 

Blue Border, No. 2. 

9. 

Patrol Lights. 

47. 

Blue Border, No. 3. 

10. 

Air Compressor Motor. 

48. 

Blue Border, No. 4. 

11. 

Exhaust Air Motor. 

49. 

Blue Border, No. 5. 

12. 

Exhaust Air Motor. 

50. 

Blue Proscenium. 

13. 

Sunlight Ceiling. 

51. 

Main House Switch. 

14. 

Orchestra Lights. 

52. 

Plug Pockets. 

15. 

Program Lights. 

53. 

35 ampere Pockets. 

16. 

Top White Main. 

54. 

35 ampere Pockets. 

17. 

Top White Foots. 

55. 

35 ampere Pockets. 

18. 

Top White Border, No. 1. 

56. 

100 ampere Pockets. 

19. 

Top White Border, No. 2. 

57. 

Curtain Motor. 

20. 

Top White Border, No. 3. 

58. 

100 ampere Pockets. 

21. 

Top White Border, No. 4. 

59. 

Dressing Rooms. 

22. 

Top White Border, No. 5. 

60. 

100 ampere Pockets. 

23. 

Top White Proscenium. 

61. 

200 ampere Pockets. 

24. 

Main White Switch. 

62. 

Picture Machine. 

25. 

Bottom White Main. 

63. 

Picture Machine. 

26. 

Bottom White Foots. 

64. 

Fifth Floor and Gallery. 

27. 

Bottom White Border, 

65. 

Fans. 


No. 1. 

66. 

4th Floor. 

28. 

Bottom White Border, 

67. 

Stage Chandelier. 


No. 2. 

68. 

Fans. 

29. 

Bottom White Border, 

69. 

Third Floor. 


No. 3. 

70. 

Hoist Motor. 

30. 

Bottom White Border, 

71. 

First and Second Floors. 


No. 4. 

72. 

Balcony Front. 

31. 

Bottom White Border, 

73. 

Balcony Front. 


No. 5. 

74. 

Paint Bridge. 

32. 

Bottom White Proscenium. 

75. 

Rigging Loft. 

33. 

Boxes. 

76. 

Fly Floor. 

34. 

Boxes. 

77. 

Fly Floor. 

35. 

Red Main. 

78. 

Pump Motor. 

36. 

Red Foots. 




Figure 101 shows a diagram of the connections of 
an elevator signalling device. The diagram is shown 
for only six floors, but it is evident that it could be 
extended to any number of floors. At each floor, 
with the exception of the top and bottom, are two 
incandescent lamps, the upper lamps (shown by light 
circles) burn when the elevator car is moving up¬ 
ward, while the lower lamps (shown by black circles) 


114 


WIRING DIAGRAMS 


burn when the car is traveling downward. These 
lamps are connected to a series of contacts, #, 3, 1\ 
etc., which are mounted on a device generally lo¬ 
cated at the top of the shaft near the elevator ma¬ 
chine. A sliding contact, which is operated by 

means of a screw geared to the 
elevator drum and so designed that 
the motion of the elevator car from 
the top to the bottom of the shaft 
will move the contact piece over 
the entire length of bar a, makes 
connection between the contacts a 
and 3 , 5 , 6, while the car is 

moving upward, and between a' 
and 1' , 3\ 5\ while the car 

is moving downward. This mov¬ 
able contact is of such size that 
connection is made to three or four 
of the contacts, 2, 3, etc., at 
one time. The operation is as fol¬ 
lows: Suppose the car is at the 
bottom of the shaft. The sliding; 
contact piece will connect a with 
contacts #, 3 and If. Current will 
then flow from the Main to the 
“up” lamps on the 2d, 3d and 4th floors. As the car 
moves upward contact is made to points, 3 , ^ and 5, 
while the contact to the 2d floor is broken. In this way 
the lamps on three or four floors ahead of the car will 



FIGURE 101. 































ELECTRIC LIGHTING 


115 


burn until the car reaches the top of the shaft. The 
last contact, 6, is of such size that it will take in the 
whole movable contact so that while the car is at the 
top of the shaft the light on the 6th floor only will 
burn and this light shows that the car is going down. 
When the car starts to move downward the connection 
between ci and 6 is broken and connection made be 
tween a' and 5V and 3\ the “down” lamps on the 
corresponding floors then burning. As the car moves 
downward the operation previously explained will be 
repeated except that the “down” lamps will burn. 


CHAPTER X. 


ARC LAMPS, NERNST LAMP, COOPER HEWITT LAMP. 

Figure 102 shows the circuits of the improved 
Brush arc lamp. This lamp is used on constant-cur¬ 
rent, direct-current systems. The current enters the 



positive binding post P and part of it goes through 
the resistance R to the carbon rods C, C, then through 
the carbons to the negative post N. The remainder of 
the current passes through wire a to the cutout block 
C, O, but, as the cutout is closed at first, the current 

.116 
































































ARC LAMPS 


117 


crosses over through the cutout bar to the starting 
resistance S, R, and to the negative side of the lamp; 
a part of this current, however, is shunted at the cut¬ 
out block through the coarse wire winding of the 
magnets M, M, and so to the upper carbon rod and 
carbons and out. The fine wire winding of the mag¬ 
nets M, M, is connected in the opposite direction to 
the coarse winding, and its attraction is therefore op¬ 
posite. When the arc increases in length, its resist¬ 
ance increases, and consequently the current in the 
fine wire is increased. The attraction of the coarse 
wire winding is therefore partly overcome and the 
armature begins to fall. As it falls the arc is short¬ 
ened and the current in the fine wire decreases. The 
fine wire of the magnets M, M, is connected in series 
with the winding of the auxiliary magnet M r . This 
magnet, which also has a supplementary coarse wind¬ 
ing, does not raise its armature unless the voltage at 
the arc increases to 70 volts. The two windings con¬ 
nect at the inside terminal on the lower side of the 
auxiliary cutout magnet and the current from the 
fine wire of the main magnets passes through both 
windings and then to the cutout block and so to the 
starting resistance and out. If the main current is 
interrupted (as by the breaking of the carbons) the 
whole current of the lamp passes through the fine 
wire circuit. This will energize the auxiliary mag¬ 
net M' and close a circuit directly across the lamp 
through the coarse wire on AT to the main cutout 


118 


WIRING DIAGRAMS 


and thence to negative terminal. When the main cut¬ 
out C, 0, operates, the armature of the auxiliary cut¬ 
out falls because there is not sufficient current in that 
circuit to energize the magnet. This lamp is switched 
off by simply short circuiting it across N, N'. 

In all direct current arc lamps care must be taken 
to see that the current enters at the proper binding 
post, as the positive carbon burns away about twice 
as fast as the negative carbon. When a lamp is burn¬ 
ing a small cup-shaped formation will be noticed at 
the arc on the positive carbon and a small projection 
on the negative carbon. Lamps are generally con¬ 
nected so that the upper carbon is positive, and this 
hollow formation on the positive will throw the light 
downward. In this way it can be determined by the 
way the light is thrown as to whether a lamp is burn¬ 
ing right side up or not. 

Figure 103 shows the circuits in a constant current 
arc lamp for use on alternating current systems. 
When the lamp is switched on current passes through 
the coarse winding of magnet M and then to the car¬ 
bon rod and carbons and out at the other terminal. 
This energizes M and attracts the core A, thus rais* 
ing the upper carbon and establishing the arc. The 
magnet ivT is wound with a great length of fine wire 
and opposes magnet M. As the resistance of the arc 
increases more current is sent around the fine, wire 
winding of M' and the core A and the carbon thus 
lowered. If for any reason (breaking of the car- 


ARC LAMPS 


119 


bons, etc.), the resistance at the arc is greatly in¬ 
creased, the core A will be lowered until the two points 
of the cutout C come in contact when the main cur¬ 
rent will pass through C and resistance R to the post 
T'. The resistance of R is in such proportion to 
that just enough current is sent around M' to keep 
the cutout C closed. By means of the spring S the 
length of the arc may be adjusted. Tightening the 
spring increases the arc by requiring a greater 
amount of current to flow around M' to lower the 


carbons. 



t r 



Figure 104 shows the winding of a constant poten¬ 
tial, alternating current arc lamp. R is a reactance 
or choking coil, the purpose of which is to cut down 
the voltage of the line to that required by the arc. 
This coil takes the place of the resistance coil in the 
















































































120 


WIRING DIAGRAMS 


direct current, constant potential lamp. The current 
passes from the binding post T to the magnets M, M, 
and then to the upper carbon, from there to the lower 
carbon and then through the reactance coil and out 
at the other terminal. It will be noticed that this 
lamp has no shunt winding similar to the constant 
current lamp. This is unnecessary as the voltage at 
the terminals is practically constant. As the carbons 
burn away the current through M, M, is decreased, 
due to the increased resistance of the arc, and the 
armature is lowered, thus lowering the carbons. 



G. 


FIGURE 105. 

Direct-current, constant-potential arc lamps differ 
from the constant-current lamps in that no auto¬ 
matic cutouts can be used, and in order to put out 
the lamp, the circuit must be opened. Constant-cur¬ 
rent larrms require no extra resistance, while con- 

























NERNST LAMP 


121 


stant-potential lamps cannot be operated without 
some resistance to steady the current. 

Figure 105 shows the diagram of a Nernst lamp. 
In the diagram, H is the heater, which is made up of 
a winding of platinum wire on a porcelain tube. The 
glower G is composed of an oxide which at the ordi¬ 
nary temperature is of very high resistance but when 
heated lowers in resistance considerably. The ballast 
B is made up of fine iron wire which increases in re¬ 
sistance as it becomes heated, thus tending to steady 
the current and keep the voltage over the glower as 
near constant as possible. When the lamp is started 
current passes through the heater H, gradually heat¬ 
ing it and the glower, which is located directly below 
it. As the glower is heated current begins to pass 
through it and the cutout magnet M, until finally it 
becomes strong enough to attract the cutout C which 
opens the heater circuit. This circuit will then remain 
open as long as current is passing through the glower. 
These lamps are made in several sizes from one to six 
glower and they consume when burning 88 watts per 
glower. Each glower is equal in candle-power to 
three ordinary 16 candle-power incandescent lamps. 
When the lamp is started more current is used than 
when the lamp is burning, owing to the fact that the 
heater coils are in circuit. In the six-glower lamp 
which takes when burning 2.4 amperes on 220 volts, 
the starting current rises to about 3.2 amperes. These 
lamps are at present used only on alternating current 


122 


WIRING DIAGRAMS 


systems as the glower becomes blackened in a short 

time when used on direct-current systems. 

Figure 106 shows a diagram of the connections 

of the Cooper Hewitt mercury vapor lamp. The 



light from this lamp is emitted from the two tubes 
T, T', which, when current is passing through them, 
glow with a greenish light. The tubes T, T', are of 
glass and the air has been extracted from them; they 
are provided at their upper ends with electrodes inside 
























































COOPER HEWITT LAMP 


123 


the tube to which leading in wires are attached and 
at the lower ends with iron cups which are partially 
filled with mercury. Either of two different methods 
are used to start the lamp. In one case a coil of 
great inductance is used to send a kick of current 
through the tube between the positive and negative 
electrodes, thus breaking down the high resistance and 
allowing current to flow. In the other method after 
the current is turned on the tubes are tipped until all 
the mercury in the lower cup flows out into the tube 
and forms a path to the upper electrode. As the 
tube is tipped back and the column of mercury leaves 
the upper electrode light is given off. The connec¬ 
tions can be easily traced. Current passing from the 
positive main flows through the cutout, switch S, to 
the positive terminal of tube T' then through tube T' 
to the negative terminal and out to the + of tube T, 
through this tube and the adjustable resistance R to 
the negative side of the line. The two tubes and the 
resistance are simply connected in series through the 
proper cutout and switch. Great care must be taken 
to see that current flows through the lamp in the 
proper direction for, if current is sent through in 
the wrong direction, even for a few minutes, the tube 
will be ruined. The type of lamp shown is used for 
photographic purposes and takes about 3. o amperes 
at 110 volts when running normally. At the start 
the current rises to a little over 100$ for a very short 
time. The ordinary lamp consisting of a single tube 


124 


WIRING DIAGRAMS 


is rated at about 750 C. P. After the lamps have 
been in use for some time (about 1600 hours), the 
inside of the lamp becomes coated with a brownish sub¬ 
stance and small globules of mercury will adhere to the 
sides. The tubes then have to be replaced. For photo¬ 
graphic purposes this lamp taking 3.5 amperes com¬ 
pares very favorably with a 10 ampere arc lamp. 


CHAPTER XI. 


RECORDING WATTMETERS. 

Figure 107 shows the circuits in the two-wire Thom-’ 
son recording wattmeter. One of the mains is con¬ 
nected through the winding M, M, which forms the 
fields of a motor. The armature of this motor is con¬ 
nected across the mains in series with a resistance R 
and the shunt field S. This shunt field is always in cir¬ 
cuit, whether there is current used through the meter 
or not, and it is so arranged that it tends to start the 
motor. Its purpose is to overcome the friction of the 
armature so that the meter will register on very small 
loads. It will be noticed that the connection for the 
potential circuit is taken off the main at A. This is 
done so that the meter will register the current used 
in the potential circuit, and this is one reason why 
the generator must always he connected on the left 
side and the load on the right side of the meter. If 
this form of meter is fed from the wrong side it will 
run backward. In Figure 107 it will be seen that if 
the feed were reversed (leaving polarities unchanged) 
the current through the fields would be in the oppo¬ 
site direction, while that through the armature would 
remain unchanged, hence the motor would be reversed. 
Used on direct-current this meter runs as a simple 

125 


126 


WIRING DIAGRAMS 


direct current motor and when used on alternating 
current, at each reversal of the current the polarities 
of both the fields and armature are changed simulta¬ 
neously; and the motor will therefore continue to 
run in the one direction, because changing the direc¬ 
tion of current in both the fields and armature of a 
shunt motor does not change the direction of rota¬ 
tion. There is no iron used in the construction of the 
motor and therefore no loss from heating. 




FIGURE 108. 


Figure 108 shows the two-wire meter for heavy 
loads. The circuits in this meter vary from the pre¬ 
ceding one only in having but one main carried 
through the meter with a tap to the other main. 

Figure 109 shows the three-wire meter. The two 
outside wires (positive and negative) are carried 
through the meter, one through each field, and the 
armature is connected from one outside to the neutral. 
In some of the three-wire meters no neutral lap is 











































































RECORDING WATTMETERS 


12V 


used, the potential circuit being connected directly 
across the outside mains. 



Figure 110 shows a meter for a balanced three 
phase line. 

Figure 111 shows a station meter for use on series 
arc lines. 

f* - 




Figure 112 shows a meter used on switchboards to 
record the entire current passing through the bus 

bars. 









































































































































128 


WIRING DIAGRAMS 


Figure 113 shows the circuits in the Gutmann 
wattmeter. This meter is used with alternating cur¬ 
rents only and depends for its action on an aluminum 
disk, slotted in spiral lines, operated in joint action 
with a shunt laminated magnet coil S' and a pair of 
series coils S, S. In the two-wire meter the series coils 
are connected in series with one of the mains and the 
shunt coil is connected across the mains as showrn in 
diagram. The loss in the shunt coil does not exceed 
\y 2 watts on the 110 volt 60 cycle meter and the drop 
in the series coil does not exceed *4 °f one volt on 
full load on the small size meters, and is proportion¬ 
ally less in the larger meters. 




Figure 114 shows the 200-250 volt meter. This 
meter has in series with the shunt coil a reactance 
coil R. 

Figure 115 shows the three wire meter. In this 
meter one of the outside mains is carried through 
one series coil and the other through the other series 






































RECORDING WATTMETERS 


129 


coil. No tap is taken to the neutral as the pressure 
circuit is connected across the mains as in the 200-250 
volt meter. 

Figure 116 shows a meter for use on either 100 or 
200 volt systems. The connection shown in the full 
lines is for 100 volts and the dotted for 200 volts. 
The reactance coil R is balanced to have exactly the 
same choke as the shunt coil. 



FIGURE 115. 



In Figure 117 the connections of an Edison chem¬ 
ical, three-wire meter are shown. The two outsides 
only are carried through the meter, no neutral con¬ 
nection being used. This type of meter was one of 
the first used on commercial work, the amount of cur 
rent having passed through the meter in a given time 
being determined by the amount of zinc deposited on 
the negative electrode. These meters are rapidly be¬ 
ing replaced by the mechanical meters. 

Figure 118 shows a diagram of what is known as 
the Wright discount or demand meter. This meter 
is used in connection with recording wattmeters to de- 




















































130 


WIRING DIAGRAMS 


termine the maximum current which has been used 
during a given time. It is also used on circuits where 
it is desired to know the maximum current which has 
passed through the circuit. In the diagram, B is a 
glass bulb connected to a tube U which is partly filled 
with a liquid. Around bulb B is wound a resistance 
wire which carries the main current. When current 
is flowing in this wire heat is generated and the air 
in the bulb is expanded thus forcing the liquid around 




tube U until it reaches the point where the tube U 
and I join, when it will flow into tube I. The amount 
of liquid in tube I will depend on the maximum 
amount of current which has passed through the re¬ 
sistance wire on bulb B. The scale back of tube I 
is graduated in amperes and watts. The meter is not 
effected by momentary increases in the current. If 
the maximum current lasts five minutes 80$ will regis¬ 
ter; ten minutes, 95$ will register; thirty minutes, 
100$ will register. 




























































RECORDING WATTMETERS 


130a 


The Wright demand indicators described in the 
previous figure, 118, are influenced only by the cur¬ 
rent and therefore cannot be used on a. c. circuits hav¬ 
ing a power factor less than unity. The demand in 
all a. c. circuits must be measured in watts and there¬ 
fore several types of demand meters have been de¬ 



veloped which are governed directly by the watt meters 
in circuit. A diagrammatic sketch of one of these is 
shown in Figure 118 a. This instrument is manu¬ 
factured by the General Electric Co. and is known 
as type P or “Printometer.” A ratchet wheel made 
of insulating material is mounted on one of the spin¬ 
dles of the register as indicated in center at top of 
figure. Two blued steel spring brushes rest diamet- 















130b 


WIRING DIAGRAMS 


rically opposite on the ratchet, thus allowing first one 
and then the other brush to drop off of the ratchet, at 
equal intervals. A platinum-iridium point is staked 
in each of these brushes, and as the brush falls off of 
the ratchet tooth, this point makes contact with an¬ 
other platinum-iridium point which is carried by a 
second spring-leaf running parallel to the brush. 
The two brushes resting on the ratchet wheel are 
charged all of the time with line potential. Thus, 
when these drop alternately upon the two leaves 
which connect to the cyclometer coil, we obtain the 
usual two-way circuit and alternately close the cir¬ 
cuit through the cyclometer solenoid. Each time this 
solenoid is energized it advances the counters one 
point. A special contact-breaking switch is provided 
as shown in upper right hand corner and its object is 
to open the circuit immediately after the solenoid has 
moved the ratchet shown in center. 

This type of demand meter is always accompanied 
with a clock "which is arranged to print the record at 
certain intervals, usually 80 minutes. This is effected 
by means of the solenoid and electric circuit shown at 
bottom of figure. When properly set up and adjusted 
this instrument will print at predetermined intervals 
a record of the number of watts consumed in the me¬ 
ter circuits during that interval and the hour of the 
day at which the energy was used. 

Another instrument devised for the same purpose 
and made by the General Electric Co. is illustrated 


RECORDING WATTMETERS 130c 

in Figure 118b. This instrument does not print a 
record but indicates the maximum amount of power 
used during a predetermined interval by means of a 
pointer. The registering device consists of a train 



of gears arranged to drive the pointer forward over 
a semi-circular dial. The gear wheels are actuated 
by a ratchet and pawl mechanism which is driven by 
an electromagnet. This electromagnet is energized 












































130d 


WIRING DIAGRAMS 


once every time a certain number of kilowatt-hours of 
electrical energy have been registered by the watt- 
hour meter. It is evident, therefore, that the position 
of the dial pointer of this demand meter is directly 
dependent upon energy consumption as registered by 
the watthour meter. 

Since the demand meter gives the demand for a 
definite time interval, it is necessary that the mechan¬ 
ism which drives the dial pointer forward over the 
scale shall be reset to zero position at the end of the 
time interval, but shall leave the dial pointer at the 
most advanced point on the dial scale to which it has 
been carried. This resetting of the register mechan¬ 
ism to zero is accomplished by a mechanism governed 
by a constant speed device so that the resettings are 
accurately timed. When used in connection with a.c. 
circuits the device is operated by a small constant 
speed motor. For d.c., clock work is used. 

The above instruments are usually set to make com¬ 
plete records of loads that last for some time. If 
the load during that time is fairly constant, they may 
be considered as giving the true instantaneous max¬ 
imum load. If the actual instantaneous value of cur¬ 
rent or wattage is wanted, some form of chart-draw¬ 
ing instrument is usually inserted in the circuit. If 
none such is at hand a curve representing with pretty 
fair accuracy the fluctuations in the circuit may be 
obtained in the following manner, which has been suc¬ 
cessfully employed by the authors: Take an ordinary 


RECORDING WATTMETERS 


130e 


sheet of paper and write upon it in straight lines the 
numbers, 1, 2, 3, etc. Let each of these numbers stand 
for seconds and let there be as many as will cover the 
time during which observations are to be taken. Let 
one man observe the disk of wattmeter and be pie- 
pared to give some signal each time the disk completes 
one revolution. Let another man hold a watch and 
count off the seconds as the watch ticks them off. A 
third man must now 7 be prepared to follow with a pen¬ 
cil the numbers on the paper in the order as the w atch 
holder reads off the seconds. With a little practice 
the man in charge of the paper will soon learn to fol¬ 
low along in synchronism w 7 ith the time indicated by 
the w 7 atch, and at every signal from the disk reader, 
make a mark upon the paper. With a few minutes 
practice three men will learn to co-operate very nicely 
in this way. The rate at which energy is consumed 
in the circuit will be inversely proportional to the 
time required for the disk to make one revolution. If 
the load carries w 7 ith it some sudden high peaks, the 
disk reader may let tw 7 o revolutions of the disk occur 
before giving the signal, but he should then have some 
distinctive signal for the marker so that he will un¬ 
derstand and mark accordingly. 


















' 

*■ - 











'j. 


















CHAPTER XII. 


DIRECT CURRENT MOTORS. 

Figure 119 shows the winding of a series motor for 
use on constant-potential circuits. In this motor the 
fields and armature are in series across the main cir¬ 
cuit. The purpose of the starting box SB is to in¬ 
sert a resistance in series with the armature when 



FIGURE 119. 


starting, to prevent an excessive flow of current which 
would result were the main current thrown on fully 
with the armature at rest. To start the motor the 
main switch S is closed, and the arm of the starting 
box is moved gradually from one contact to another 
until it has reached the position where no resistance is 
left in circuit. It is then held by means of the small 
magnet M in this position until the current is cut 
off, or for some reason ceases to flow, when, by means 

131 







































132 


WIRING DIAGRAMS 


of a spring attached to it, the arm will fly back to its 
original position. This makes it impossible to throw 
the current on while all the resistance is out of the 
armature circuit. The small magnet M is connected 
directly across the mains, generally having a resist¬ 
ance in series with it to reduce the voltage on the 
winding. This resistance is placed in the starting 
box, and is not shown in the drawing. In some motors 
the automatic coil M is connected in series with the 
main current, but in this case the variations in the 
current from no load to full load make its use unsat- 

isfactorv. 

%/ 

The speed of a series motor varies with the load, 
decreasing as the load increases and vice versa. If 
the load is entirely removed the motor will run away, 
unless, as in the case of very small motors, the ohmic 
resistance of the field and armature is sufficient to 
control it. This type of motor is also used on street 
£ar work, although in this case the starting box is re¬ 
placed with a controller which, by varying the resist¬ 
ance or connecting the motors in series or multiple 
(where two motors are used), varies the speed. [See 
Figure 127.] Reversing either the field or armature 
connections will reverse the direction of rotation. If 
the field and armature are both reversed the motor will 
run in the same direction. 

This motor is always protected from overload by 
a fuse or circuit-breaker placed in the main circuit. 
Fuses are shown in the drawing on the motor switch. 


DIRECT CURRENT MOTORS 


133 


Figure 120 shows the winding of a shunt motor. 
The field and armature of this motor are placed in 
shunt across the main circuit. The starting box SB 
is placed in the armature circuit and performs the 
same service as in the constant-potential, series motor. 
The automatic coil of the starting box is connected in 
series with the field circuit. The speed of a shunt 
motor is practically constant, and for this reason this 
type of motor is extensively used. The motor is 



FIGURE 120. 


started in the same way as the series motor, and is 
protected from overload in the same way. If either 
the field or armature connections are reversed the mo¬ 
tor will run in the opposite direction. The speed of 
a shunt motor may be varied by inserting resistance 
in either the armature or field circuit [See Figure 
124], or by shifting the brushes. 

It must also be remembered that the loss in the 
line in long runs feeding a motor will cut down the 
P. D. at the armature, and this will decrease the speed 











































134 


WIRING DIAGRAMS 


as the load increases. To obviate this the size of 
wire should be chosen so that the drop in potential 
shall be as small as possible. 

Figure 121 shows the winding of a compound mo¬ 
tor. In addition to the shunt winding on the fields 
an extra winding is added, which is in series with the 
armature. The starting box is connected in series 
with the armature, and the automatic coil M is con¬ 
nected in series with the shunt field as in the shunt 



motor. The series winding of these motors is con¬ 
nected in either of two ways, known as the “cumula¬ 
tive” or “differential.” The winding shown in the 
diagram is cumulative, the current in the shunt and 
series winding being in the same direction. In the 
differential winding the current in the series coil trav¬ 
els in an opposite direction from that in the shunt 
coil. 

Motors having the differential winding will main¬ 
tain a more constant speed; for, as the load increases, 






























DIRECT CURRENT MOTORS 


135 


the increased current in the series winding will partly 
neutralize the effect of the shunt winding and decrease 
the magnetism of the field, thus tending to increase 
the speed of the motor. On loads which have a con¬ 
stant variation, such as the planer, for instance, when, 
at the end of each stroke a great increase of load 
comes on, the differential motor is apt to spark badly. 
The cumulative motor will in the same case slightly 
decrease in speed at each stroke. The differential 
motor is not as efficient as the cumulative form from 
the fact that there is a waste of current due to the 
two fields opposing each other. 

Where motors are used in isolated plants the motor 
switches should be opened before the plant is shut 
down. 

A number of different connections by which the 
speed of a motor may be varied or the direction of 
rotation reversed, are shown in Figure 122. Where 
the three-wire system is in use the speed of a motor 
may be varied by using the three-wire, double-throw 
switch shown at the left of the diagram. With the 
switch thrown to the upper position the armature will 
obtain the full line voltage, and with the switch on the 
lower position the armature will receive the voltage 
between the outside and the neutral; while the field 
will receive in both cases the full voltage of the line. 
In the 110-220 volt system the upper connection 
gives 220 volts and the lower connection 110 volts on 
the armature, the field receiving 220 volts. It is cus- 


\36 




WIRING DIAGRAMS 


tomary to use a three-wire, single-throw switch to 
connect the service to the motor, this switch bein# 





placed in the line before the double-throw switch and 
being used whenever it is desired to shut down the 


FIGURE 122. 






































DIRECT CURRENT MOTORS 


137 


motor. The double-throw switch is only operated 
when the motor is at rest. 

In the upper part of the diagram are shown the 
connections of the Cutler-Hammer underload and 
overload starting box. With the movable arm A on 
contact shown in drawing no current will flow. If 
the arm is moved to contact 1 current will flow from 
the main through magnet U to the arm A, through 
all the resistance to the series field and armature and 
to the other side of the line. As soon as the movable 
arm has made contact with 1, current will also flow 
through the winding of magnet M and out to the 
shunt field and opposite side of line. The arm A is 
gradually moved to the right until it reaches the last 
contact, where all the resistance is cut out of the 
armature circuit. When it reaches this point the 
magnet M, which is energized, attracts the armature 
on the arm A and holds it in this position as long 
as current is flowing through the magnet. 

If the main supply were for any reason shut off, 
the magnet M would be de-energized, and the arm A 
(which is equipped with a spring) would fly back to 
the “off” position. This makes it impossible for the 
supply current to be momentarily cut off and then 
thrown on again while all the resistance is cut out of 
the armature circuit. In case the field circuit should 
open, by the breaking of a wire, for instance, the 
magnet M would be de-energized and the current cut 
off. When the motor is shut down by opening the 


138 


WIRING DIAGRAMS 


motor switch, the arm A will not fly back until the 
speed of the motor has considerably decreased, owing 
to the fact that the motor is acting as a generator and 
sending current around the shunt field and coil M. 

The purpose of the magnet U is to protect the mo¬ 
tor from any excessive rise in current, due either to 
a short circuit in the motor or to the throwing on of 
too heavy a load. With the normal current flowing 
through the winding of U, the armature below T it wdll 
not be attracted; but if the current exceeds a certain 
amount the armature is attracted, and the winding of 
the automatic magnet M short-circuited at the point 
P, thus demagnetizing M and allowing the arm A to 
fly back and shut off the current from the motor. 
The armature below magnet U is adjustable, so that 
it may be set to operate at whatever current is de¬ 
sired. 

Similar apparatus to the above may be used to 
regulate the speed of the motor by applying resist¬ 
ance in series with the armature, and thus cutting 
down the current; but in such case the apparatus is 
designed to carry the full current for an indefinite 
time. The automatic coil M is arranged to attract 
an armature which is connected to a pivoted lever, 
having a point at the other end which fits into a series 
of indentations on the low r er part of arm A, and holds 
the arm squarely over the contacts in whatever posi¬ 
tion it may be placed for the required speed. 

Strengthening the field of a motor tends to decrease 


DIRECT CURRENT MOTORS 139 

the speed, and weakening the field to increase the 
speed. SR is a rheostat connected in series with the 
shunt field by means of which more or less resistance 
may be cut in series with the fields. Cutting in more 
resistance will reduce the current in the fields, and 
thus weaken them and increase the speed, and cutting 
out resistance will act in the opposite way. 

The two-pole, double throw switch shown in lower 
right-hand corner may be used to reverse the direc¬ 
tion of rotation of the armature. With the switch 
thrown to the upper contacts the current will enter 
the armature from the right-hand side, and with the 
switch thrown to the lower contacts current will enter 
on the left-hand side of the armature, thus reversing 
the direction of rotation. This switch should never 
be thrown while the motor is running, but should be 
thrown over while the armature is at rest. 

Figure 123 shows connections for the Cutler-Ham¬ 
mer printing-press controller, as used with a shunt 
motor. R is a resistance box generally in the larger 
size motors installed separately from the controller, 
and connected to it by wire leads. The automatic 
coil M is connected in series with the field circuit, and 
when current is on attracts an armature (not shown 
in drawing) which is connected to a pivoted lever, the 
other end of which fits into a series of indentations 
on the lower end of the arm A and holds the arm in 
whatever position it may be placed.. The arm A is 
made in two pieces, separated by an insulator so that 



140 


WIRING DIAGRAMS 


the upper and lower parts are not in electrical con¬ 
nection. As the arm is moved to point 1, current 
from the mains enters the lower part of the arm and 
goes to the copper segment S. From there it is car¬ 
ried to the armature and back to the segment T. It 



then crosses the upper part of the arm to the contact 
1 and through all the resistance in R and back to 
point 10 to the other side of the line. The field is 
simply connected across the mains through coil M. 
If the arm A is moved to point 1, the current will 
then flow through the armature in the opposite direc¬ 
tion, thus reversing the direction of rotation. With 
the arm on contact 10 all the resistance is cut out of 
the armature circuit. This controller has ten varia¬ 
tions in speed forward, and two backward. At the 

























































DIRECT CURRENT MOTORS 


141 


left is shown a diagram of the connections of this 
starting box when used with a compound motor. 

In Figure 124 are shown connections for the Cutler- 
Hammer self-starter used with a motor driven pump. 
The connections shown are for a compound motor. 



S is a solenoid connected across the mains through the 
switch P and the arm A of the self-starter. The 
current in this circuit varies from 54 to 1 ampere, 
according to the size motor used. The sw itch P is 
controlled by a float in the tank, and is so arranged 
that it will close as the level of the water lowers and 
open again when the tank has become filled. This 






























































142 


WIRING DIAGRAMS 


switch may be placed any distance from the m<»tor. 
When the switch P closes, the solenoid S is energized, 
and the core, at the lower end of which is attached a 
copper contact piece, closes the contacts E, E', thus 
allowing current to flow through the series field and 
armature of the motor and through all the resistance 
in the starter. At the same time, when E E' is closed 
current passes through the solenoid S' and through 
the small spring connecting contacts B B'. This 
energizes the solenoid S' and draws up the core and 
arm A, thus gradually cutting resistance out of the 
armature circuit. When the arm reaches the upper 
contact, the circuit through the solenoid S' is opened 
at B and the lamps thrown in series with it. This is 
done to cut down the current flowing through the 
solenoid, as less current is required to keep the arm 
in place than to move it over the contacts. The cir¬ 
cuit from the small solenoid S is connected to the 
contact 1 so that when the arm A moves upward 
lamps are thrown in series with this circuit, to cut 
down the current in the solenoid S to that required 
to just hold it; so that, if for any reason the supply 
current is cut off, the contact E E' cannot be closed 
until the arm A has moved to the lower point, where 
all the resistance is in the armature circuit. The num¬ 
ber of lamps used varies with the size of motor. This 
same apparatus can be used with any air pump, or 
elevator in which the motor does not reverse, the 
switch P being replaced with the necessary switch. 


DIRECT CURRENT MOTORS 


143 


On the solenoid S the small magnets K are used to ex¬ 
tinguish the arc at the break. 

Figure 125 shows a diagram of the connections of 
a shunt motor used for blowing a pipe organ. The 
arm of the resistance box R is mechanically connect¬ 
ed to the bellows of the pipe organ so that its posi¬ 
tion is determined by the amount of air in the bellows. 
When all of the air is out of the bellows the arm of 



the rheostat is in the position where no resistance is 
in circuit, or as shown in the diagram. As the motor 
speeds up and air is forced into the bellows the rheo¬ 
stat arm slowly moves over the series of contacts cut¬ 
ting resistance into the circuit at each step. When the 
bellows are completely filled the arm is on the last con¬ 
tact where all of the resistance of the box R is in 
series with the motor, this resistance being great 








































144 


WIRING DIAGRAMS 


enough to completely stop it. From the above de¬ 
scription it will be seen that the action is automatic, 
the speed of the motor being governed by the amount 
of air taken by the organ. After the organ has been 
at rest for some time the air gradually leaks out of 
the bellows and the rheostat arm moves to the point 
where no resistance is in circuit. For this reason a 
starting box is always provided. 

Figure 126 shows the connections of the Cutler- 
Hammer compound drum controller, this type of con¬ 
troller being used on printing presses, cranes and 
other work requiring a frequent change in speed and 
direction of rotation. In the upper part of the dia¬ 
gram is shown the drum laid out, the contact rings 
X, Y, Z, Y', Z' and W, and the segments below being 
mounted on a revolving drum, while the contacts 1 to 
7 and B, A, SF, B r A', SF' and L are stationary, 
being supplied with fingers which make contact with 
the segments opposite as the drum is revolved. 

With the drum moved to the first point on the for¬ 
ward motion the rings X, Y, Z will come in contact 
with A, SF and 1 respectively, and the rings W, Y' Z' 
with B', SF' and L. Current will then flow from the 
-f- main through the series field to the resistance box 
R and through all the resistance to the point 1 of the 
controller. From 1 it passes to contact ring Z, and 
then through ring X and contact A to the armature 
and back to B' and ring W to ring Z' and contact L 
to the negative side of the line. As the drum is moved 


DIRECT CURRENT MOTORS 


145 



FIGURE 126 








































































































































































146 


WIRING DIAGRAMS 


toward point 7 at each step, part of the resistance 
in series with the armature is cut out, until at 7 the 
armature and series field are connected directly across 
the mains. 

In the bottom of the controller are located two cop¬ 
per rings and a number of contacts, which are con¬ 
nected to their respective points in resistance box R. 
A small, movable contact shoe short-circuits rings 11 
and 17, while the controller is moved from points 1 
to 7, thus allowing current to pass from the positive 
side of the line to 17, on to 11, and then through 
the shunt field and out to bar Y' on controller and 
to negative side of line. As the drum passes point 7 
the contact shoe connecting 17 and 11 will then con¬ 
nect 17 and 12, thus cutting the resistance between 
points 11 and 12 in the resistance box R in series 
with the field and increasing the speed of the motor. 
As the controller is moved still further, more resist¬ 
ance is cut in series with the field, until at point 14 
all the resistance is cut in and the motor has reached 
its highest speed. 

If the drum is moved to 1 on the reverse motion 
the same connections are made with the exception of 
the armature. In this case current from contact 1 
passes to ring Z' and then to B and armature, this 
causing current to flow in the opposite direction in 
armature and reversing the direction of rotation. In 
printing press work a stop is used which allows the 


DIRECT CURRENT MOTORS 


147 


reverse motion to take in two contacts only, thus limit¬ 
ing the reverse to two speeds. 

Figure 127 shows the connections of the General 
Electric K2 street car controller. This controller is 
of the series parallel type, and varies the speed of the 



FIGURE 127. 


car by connecting the motors first in series and then 
in parallel, suitable resistance being used to give a 
gradual starting current. In Figure 128 are shown 
the various connections between the rheostat and mo¬ 
tors obtained at the different points of the controller. 
In the upper left-hand corner the drum of the con¬ 
troller is laid out. T, Rl, R2, etc., are stationary 















































































































































148 


WIRING DIAGRAMS 


contacts with fingers which make contact with the va¬ 
rious segments on the drum as it is revolved. 

At the right of the controller is the reversing 
switch, by means of which the car can be made to go 
in either direction. The reverse switch is also a drum 
on which are placed two sets of contacts, these making 
connection with the stationary points F2, AA2, etc., 
as the drum is revolved. If the controller drum is 
moved to point 1, the current from the trolley wire 
enters at T, then to segment on drum opposite T. 
From there it passes to contact Rl, then to rheostat 
K, through all the resistance to the point 19 on the 
reverse switch. With the reversing switch on F it 
will then pass to Al, through the armature of motor 
No. 1 back to AA1, on the reverse switch and through 
field of motor No. 1 to the point El on the controller. 
From El it passes to the point 15 by means of seg¬ 
ments on the drum, and to 15 on the reversing switch 
and to armature of motor No. 2 back to AA2 on the 
reversing switch, and to the field of motor No. 2 and 
back by means of E2 to the ground. The two motors 
are now connected in series with all the resistance in 
rheostat K in series with them. This is shown in 1 
of Figure 128. 

As the controller is moved to points 2 and 3, part 
of the resistance in rheostat Iv is cut out, until at 4 
the two motors are running in series with no resist¬ 
ance. At point 5 the fields of both motors are weak¬ 
ened by shunting them around the resistance in rheo- 


DIRECT CURRENT MOTORS 


149 


stat K2, thus further increasing the speed. The 
points between 5 and 6 are used to change the con¬ 
nections from series to multiple. At point 6 the mo¬ 
tors are in multiple, in series with part of the resist¬ 
ance in K. At points 7 and 8 part of this resistance 
is cut out, while at 9 the motors are connected in 
multiple with the fields weakened. 


^MfftSTUT K 


W4T 


J" 


1 


-*0“— I W\AAA i - 


O 


-o 


o 


o 


o 

o 


t=Q: 


O 


AAAAA- 


-AA/W- 
—AVW— 

T J Wl 

f, SHUMT LI 

—AAAAA- 


O 

O 


-o 


-o 


o 


AAAAA- 


■O 


O-W/V^r—C> 




-O-VW— f rO- 


3—j-Q ■■ — VvW—^—O 


FIGURE 128. 


AMAA 1 


-MMA- 


A/V\AA 




AAAAA- 


h" "jHuWt T 


aaaaa- 


AAAAA 


AWA 


AAAAA 


AAAAA 


AAMA 


w- 


In case it is necessary to cut out one of the motors, 
this may be done by means of the switches shown be¬ 
low the controller. If the switch at the left-hand is 
thrown to the upper contacts, motor No. 1 will be 
short-circuited. Throwing the other switch up short 
circuits motor No. 2. When one of the motors is cut 
out, a stop comes into play which allows the controller 










































































































































































150 


WIRING DIAGRAMS 


to move over the first five points only. If this were 
not done and the controller moved to point 6, the 
trolley would be directly connected to ground through 
the rheostat K. This can be seen by reference to 6 in 
Figure 128, where cutting out motor No. 1 short- 
circuits 19 and El. The car should never be run 
with the resistance in rheostat K in circuit, therefore 
points 4, 5, 8 and 9 only should be used for any great 
length of time. The diagram shows one set of con¬ 
trolling apparatus only, this set being duplicated at 
the other end of the car. 

The speed of a constant current series motor varies 
with the load, decreasing as the load becomes greater 
and increasing in speed as the load becomes lighter. 
If the load is entirely removed the motor will “run 
away.” No satisfactory method of winding has been 
devised which would make these motors self-regulat¬ 
ing, so that if the motor is to be used on a varying 
load some mechanical device must be employed to 
regulate the speed. 

In Figure 129 the arm A moves over a series of 
contacts which are connected to different points of 
the field winding. This arm may either be moved by 
hand, or, as is more common, connected to a centrif¬ 
ugal governor. As the load on the motor increases, 
its speed will slightly decrease, thus decreasing the 
speed of the governor and moving the arm upward. 
This cuts out part of the field winding and speeds up 
the motor. 


DIRECT CURRENT MOTORS 


151 


In Figure 130 the arm A moves over a number of 
contacts which are in connection with the resistance 



wire R. Current coming from the left-hand main 
passes through the lower part of the resistance R 
and is shunted at the arm A, part ot it passing 



through the remaining resistance and pait of it going 
to the motor. By changing the position of the arm, 













































152 


WIRING DIAGRAMS 


more or less current can be sent through the motor, 
the greatest amount passing through it when the arm 
is at the lowest contact. The arm may either be 
moved by hand or used with a centrifugal governor, 
as described in the preceding paragraph. It will be 
seen that this method is not very efficient, as a great 
deal of energy is consumed in the resistance wire. 
There are a number of other methods used for con¬ 
stant current series motor regulation, but they are 
mostly variations of those shown. 

This type of motor is fast being replaced by the 
constant potential motor. Fuses are never used on 
these motors, as the current is always the same, and 
the switch used to start and stop the motor closes 
the main line when it opens the motor circuit. The 
ordinary snap switch cannot be used. 

Figure 130a shows diagram of a printing press con¬ 
troller generally known as of the Kohler system and 
built by the Cutler Hammer Co. This system is 
widely used and there are many variations; modifi¬ 
cations being made in some cases to fit different volt¬ 
ages and also to obtain different results as not all 
presses are run in the same way. 

In the diagram M is the main magnet which when 
energized closes the armature circuit at A. The two 
circles below A represent blow out magnets which are 
not always used. The circuit can readily be traced 
along the heavy lines and through the rheostat R. 
N is another magnet or solenoid which when energized 



DIRECT CURRENT MOTORS 


153 



FIGURE 130a. 








































































































































154 


WIRING DIAGRAMS 


pulls up the contact bar of the rheostat R until it rests 
as indicated by dotted lines, thus cutting all of the 
resistance of R into the armature circuit. 

When at rest in any position the solenoid is held in 
place by a ratchet device (not shown) and also by cur¬ 
rent which passes through N and the auxiliary resist¬ 
ance L at the left. The ratchet and also the circuit 
through N are controlled by another magnet O. This 
magnet when energized withdraws the ratchet and 
allows the bar to slip down and also opens the circuit 
through N. at 5. When the circuit of O is closed the 
solenoid N begins to move downward cutting out resist¬ 
ance until the circuit of O is opened when it comes to 
rest wherever it happens to be. Thus more or less of 
the resistance R may be left in the armature circuit. 

The field circuit F can readily be traced and it can 
be seen that as the solenoid moves down to its lowest 
notch resistances are cut into the field circuit which 
weaken the field and cause the motor to attain its 
highest speed. 

B is the brake circuit and when M descends after 
being deenergized it closes the armature circuit at B, 
thus short circuiting the armature and quickly bring¬ 
ing the motor to rest. 

C is a circuit breaker and the plunger shown opens 
the circuit through M wdien the armature current ex¬ 
ceeds its allowable value. 

The various buttons by which the motor is controlled 
are showm in the lower right hand corner. There may 


DIRECT CURRENT MOTORS 


155 


be any number of these buttons and they may be 
located at different convenient places about the ma¬ 
chinery. From any one of these buttons the motor 
may be started or stopped. The operation is as fol¬ 
lows: The motor cannot be started unless the solenoid 
N has drawn up the contact bar of the rheostat to its 
highest point closing the safety circuit at S. This is 
accomplished as soon as the main switch (not shown) 
is closed. Current passes from the positive pole of 
the circuit to point 1 which is closed until M is ener¬ 
gized, thence through N to point 2 which is closed until 
N has acted, and from there to the negative pole of 
the line. 

The middle bar at 5 rests upon the lower contacts 
there shown except when O is energized. When O is 
active this bar is drawn up against the upper contacts. 
Before current can be gotten into the armature circuit 
all of the points 3 on the buttons must be closed. 
When this is done circuit is established through wire 4, 
magnet M, resistance P and the negative pole of the 
line. Owing to resistance P this current is not of 
sufficient strength to close the armature circuit at A. 
When now one of the buttons is closed at 6 current is 
established through O to the negative pole of the line. 
This releases the ratchet before mentioned and also 
draws up 5, establishes a shunt circuit around P through 
S and strengthens the current in M sufficiently to draw 
up the core and close the armature circuit at A. This 
starts the motor at its slowest speed and allows the 




156 


WIRING DIAGRAMS 


contact bar of R to descend, thus cutting resistance 
out of the armature circuit and speeding up the motor. 
When the button 6 is released 5 again closes the circuit 
through L and holds N wherever it may be, thus 
keeping the motor running at that speed. 

If the speed of the motor is to be reduced pressing 
one of the buttons 7 will cause the contact bar of N to 
rise and cut in more resistance into the armature cir¬ 
cuit. The motor can be stopped by opening any one 
of the buttons 3, but all of them must be closed before 
it can be started. This is a safety arrangement of 
great value. 

Another diagram of Kohler system printing press 
controller is given in Figure 130b. In this case the 
motor is reversible but can be used in the reverse 
direction at the slowest speed only. There is also a 
lock mechanism shown at P which can be set so that 
the motor can be operated at a fixed speed only. In 
this case it is intended that the pressman shall have 
no control over the speed but have full control over 
starting and stopping of motor. 

The field and armature circuits can easily be traced 
and will need no explanation. There is also the brake 
circuit as in the preceding Figure 130a. 

With the reversing switch indicated in the lower 
right hand corner thrown to the right, circuit is at once 
established through wire 1 solenoid N points 2 and 3, 
and the negative pole of the line. When N acts the 
circuit at 2 is opened and current is now forced through 


DIRECT CURRENT MOTORS 



FIGURE 130b. 


IH UI Ml 



























































































































158 


WIRING DIAGRAMS 


R' which reduces it so as to be only sufficient to main¬ 
tain N in its position. With the reversing switch 

V 

thrown to the left there is current in N only while 
button 4 is closed and when this is opened the contact 
bar descends until it strikes the locked plug P the 
position of which determines the speed at which the 
motor shall run. 

To close the armature circuit it is necessary to close 
button 5. This sends current through point 6, sole¬ 
noid M, safety S, point 3 and negative pole of line. 
There is also a parallel circuit around the circuit 
breaker C which keeps the circuit open after an over¬ 
load in the armature circuit has caused the breaker to 
act. For normal operation in the forward direction 
button 4 must be closed and remain closed until 5 is 
closed. When 5 is closed the armature circuit is closed 
and the motor starts at its slowest speed. To speed 
it up 4 must be opened; this allows N to descend and 
out resistance and speed up the motor. 


CHAPTER XIII. 


AUTOMOBILES. 

ELECTRIC AND GASOLINE, CHARGING STATIONS, GAS 

ENGINES. 

The following diagrams illustrate some of the 
methods of electric automobile wiring employed by 
the Woods Motor Vehicle Co., and much of the in¬ 
formation herein given is taken from Mr. C. E. 
Wood’s work, “The Electric Automobile.” 

Figure 131 shows one of the earlier methods and 
gives three speeds. The first speed is obtained by 
grouping the batteries four in parallel and ten 
in series. This connection is made when the control¬ 
ler connects all of the points along line a with the 
opposite points along line b. The circuit can readily 
be traced, the current passing from the + poles of the 
cells to bar 1, thence to Y, through both fields, F, to 
the reversing switch R; back to both armatures, 
through other side of reversing switch and to X, 
bar 2 and the — side of the batteries. 

The second speed is obtained when the controller 
connects the points along line a with those along e. 
This places the battery in groups of two in parallel 
and twenty in series. The third step, by connecting 

159 


160 


WIRING DIAGRAMS 


a and d , places all forty cells in series with the fields 
and armatures. 



Figure 132 shows an arrangement giving four 
speeds and in which not so many changes are made 
in battery connections, but more in those of the fields. 
As in the previous diagram both armatures always re¬ 
main in parallel. 


























































































AUTOMOBILES 


161 


The first speed is obtained when the controller con¬ 
nects the points along a with those along b. The two 
halves of battery are now in parallel and work 
through both fields in series, the current passing from 



the positive pole of battery to bar 1, thence to field 
F, back to controller and through F', thence back to 
reversing switch R, through both armatures and again 
through reversing switch and back to negative pole 
of battery and bar 2. 


























































































































162 


WIRING DIAGRAMS 


The next step on the controller combines a and < 
and leaves batteries still in parallel and at the sai-ie 
time throws the fields in parallel thus weakening the 
fields and speeding up the motor. 

The third step, combining a and d, throws the bat¬ 
teries all in series and the fields also, increasing speed 
through increased E. M. F. 

In the fourth speed, connecting a and e , the bat¬ 
teries remain in series and the fields are again placed 
in parallel. The charging plug is shown at the right 
and to charge, the batteries are thrown in series. Con¬ 
nections for electric gong and lamps are also shown. 

It will be noticed that with these motors fuses or 
circuit breakers are not used. It would indeed be 
quite dangerous to have a fuse blow out when climb¬ 
ing a steep hill. The whole wiring is therefore so de¬ 
signed that it can safely carry for a short time all 
that the battery can deliver. These diagrams show 
no resistances used as with other motors; the reduc¬ 
tion of E. M. F. at starting by placing cells in paral¬ 
lel is far more economical and satisfactory. Vehicles 
have, however, been built which combine resistance 
control with the methods just described. 

Figure 133 shows the arrangement of an automo¬ 
bile charging station. By means of the rheostat R 
the current is regulated to the needs of the battery. 
The charging plug P is usually so made that it can 
be inserted only one way so that the polarities of the 
charging dynamo and the batteries will always be cor- 


AUTOMOBILES 


103 


rect. The voltmeter may be used to test the condi¬ 
tion of the battery and also to indicate polarity of 
dynamo or 

double-throw switch shown is needed only in case it 
is desired to test or “form” batteries. It provides an 
easy connection for discharging batteries. 


battery if these are not known. The 



FIGURE 133. 


In Figure 134 is shown the general principle of 
ignition used in gasoline automobiles. A jump spark 
is almost invariably used and this is produced by 
means of an induction coil capable of giving a very 




FIGURE 134. 


high voltage. The figure shows an induction coil 
equipped with a vibrator, but this is not always used 
and many equipments dispense with it entirely. The 
cam C is connected with the gearing and adjusted so 
that it makes and breaks the circuit at just the proper 






















































164 


WIRING DIAGRAMS 


time for ignition. Whenever the current at C is 
broken a spark occurs at X. At this point a “spark 
plug” equipped with proper terminals across which 
the spark is to jump is fitted into the end of the cylin¬ 
der. 

Figure 135 shows a four-cylinder engine equipped 
with four sets of batteries and independent coils. 



An arrangement using either battery or generator 
is shown in Figure 136. Generators used in this con¬ 
nection are usually fitted out with some form of gov¬ 
ernor which keeps them running at a sufficiently uni¬ 
form speed to allow of practical operation whether the 
car be running fast or slow. This figure also shows 
wiring arranged for a “double spark gap.” A spark 
plug is very apt to “foul”; that is, to become covered 
with soot from the combustion of gas in the cylinder. 
When it is thus “fouled” the current leaks through 
the carbon from one terminal to the other and, of 













































































AUTOMOBILES 


165 


course, there is no spark. The proper remedy is to 
either provide a new plug or clean the old one. It is, 
however, claimed by some automobile users that if an¬ 
other spark gap be introduced in series with the one 
which is “fouled” that both will then spark. Whether 



this be true or not it can at best be only a temporary 
relief, for in time the plug in the cylinder will be¬ 
come so completely covered that it cannot possibly 
spark. The throw-over switch in Figure 136 admits 
using a single or double spark gap. 


* —c ~- 



1 

I 

-t 

Ih ' 



FIGURE 137. 


In Figure 137 are shown the connections of a gas 
engine igniter where the gas engine is used to drive 
a dynamo supplying electric lights. The current is 
taken from an electric light circuit while the dynamo 
is running, a 50 c. p. lamp being placed in series with 






























































166 


WIRING DIAGRAMS 


the spark coil. While the engine is starting the bat¬ 
tery is used to supply current for igniting the gas. 
The single-pole throw-over switch is arranged to make 
connections either way. This arrangement has the 
disadvantage that it usually “grounds” the electric 
light system and is therefore not approved by most 
insurance companies and inspection bureaus. 



Figure 138 shows another arrangement of gas en¬ 
gine ignition. The small generator G is coupled to 
the gas engine and driven by it. While the engine 
is at rest the armature of the magnet M closes the 
battery circuit on the spark coil and cylinder C of 
the engine. As the engine gains speed the generator 
G sends current through the magnet M and raises 
the armature, thus disconnecting the battery and clos¬ 
ing its own circuit on the spark coil. If a storage 
battery is used it may be charged from time to time 
by throwing the switch S' over. The switch near C 
may be opened to prevent accidental short circuits 
while the engine is at rest. 




































AUTOMOBILES 


166a 


Figure 138a shows a typical wiring diagram of an 
automobile ignition circuit. The electrical system 
consists of a magneto geared to the engine drive shaft. 
There are two windings on the armature, a piimary 
or low-voltage winding and a secondary or high-volt¬ 
age winding. A circuit-breaking device, which is op¬ 
erated mechanically at each revolution of the arma¬ 



ture, is attached to the armature shaft. A condenser, 
also on the armature, is connected directly across the 
circuit-breaker terminals. When the automobile is 
started the starting switch SS is closed and the cir¬ 
cuit is completed through the dry batteries, intensify¬ 
ing coil and primary winding of the armature. When 
operated at the low speed of starting, the current gen¬ 
erated by the magneto is not sufficient to produce a 
suitable spark and the generator current is therefore 
intensified by the dry batteries. The circuits in start- 




























166b 


WIRING DIAGRAMS . 


ing are as follows: Through the primary winding 
of the armature and through the circuit breaker which 
is closed. Paralleled with this is the battery circuit, 
through the intensifying coil IC, and then by means 
of the brushes BB through the circuit breaker CB. At 
the proper time for ignition the circuit breaker opens 
and the combined currents of the magneto and dry 
batteries induce a current in the secondary winding 



FIGURE 138b. 


of the magneto, this winding acting as the secondary 
of a transformer. The induced, high-voltage current 
passes out through the brush B and by means of the 
distributor D to the proper cylinder. The secondary 
winding also generates a current which is added to 
that induced by the current in the primary winding. 
It is necessary to connect the battery so that the cur¬ 
rent flows in a certain definite direction through the 
circuit breaker, otherwise it will tend to neutralize the 
effect of the current generated by the magneto. The 
switch shown at K is operated by the insertion and 





















AUTOMOBILES 


166c 


extraction of a key. When the key is withdrawn the 
switch is closed to ground and the circuit breaker is 
therefore shunted directly across and made inopera¬ 
tive. The insertion of the key opens this switch and 
permits the circuit breaker to perform its proper 

function. 

Figure 138b shows the wiring diagram of an igni¬ 
tion system using, in place of the secondary w hiding 
on the armature of the magneto, an induction coil. 
The electrical action is similar to that described in 
Figure 138a except that the breaking of the magneto 
circuit induces a high-voltage current in the secondary 
of the induction coil. The condenser shown in both 
of these diagrams is provided to reduce the destruc¬ 
tiveness of the arc which occurs when the circuit is 
opened at the circuit breaker. There are many varia¬ 
tions of the circuits shown, but the principle is the 

same in most of them. 










CHAPTER XIV. 

% 

DIRECT CURRENT GENERATORS, COMPENSATORS, 

ALTERNATORS. 

A diagram of the circuits in the Western Electric 
Co.’s series arc dynamo is shown in Figure 139. Con¬ 
stant-current, series dynamos, like the constant-cur- 
rent, series motors, are not self-regulating, so that 
some mechanical means must be employed to keep the 



current constant. This is accomplished by shifting 
the location of the brushes, or varying the number of 
exciting turns on the fields, or in some cases by both 
these methods combined. In the machine shown the 
voltage is regulated by shifting the brushes. In the 
diagram, current flows from the lower or positive 
brush to the center connection of switch S, and then 
around the fields and out to the positive side of the 

167 




























































































168 


WIRING DIAGRAMS 


line, returning through the regulator R to the upper 
brush. The switch S is used in starting and shutting 
down; in the position shown switch is set for running. 

When it is desired to shut down, the switch S is 
closed. This first short-circuits the fields and then 
the armature. The switches shown at the left are 
used to cut down the current by short-circuiting part 
of the field windings. They are used where it is de¬ 
sired to operate either the 1200 c. p. arc lamp taking 
6.8 amperes, or the enclosed arc lamp taking 6 am¬ 
peres. With the switches in the position shown the 
machine will generate 9.6 amperes, the current gen¬ 
erally used on the 2000 c. p. arcs. To reverse the 
direction of current the armature leads are reversed. 
In connecting two arc machines in series the -f- of 
one machine is connected to the — of the other. The 
positive side of the machine must always be connect¬ 
ed to the positive side of the line. 

Figure 140 shows the connections on a shunt- 
wound dynamo. The winding varies from that of 
the series dynamo in having the field magnets, which 
are wound with a great length of fine wire, connected 
in shunt across the dynamo brushes. The current in 
this field is then in shunt with the main circuit, and 
is generally about 2 or 3 per cent, of the whole cur¬ 
rent generated by the machine. Shunt-wound dyna¬ 
mos are used where a current of constant potential is 
desired, such as the lighting of incandescent lamps 
in parallel, furnishing power for motors and in stor- 


DIRECT CURRENT GENERATORS 169 


age battery charging and electro-plating. Although 
the voltage of a shunt dynamo is practically con¬ 
stant, still, as the load is increased, the voltage will 
gradually fall, and this must be regulated by means 
of the rheostat R which is connected in series with 
the field. If resistance is cut out of the rheostat the 
current in the fields is increased, and the voltage of 
the machine rises, and vice versa. This dynamo is 
always protected from overload by a fuse or circuit- 
breaker placed in the main circuit. 



To start the dynamo it is first brought up to speed 
and the voltage regulated by means of the rheostat 
R and the voltmeter V, and the main switch is then 
thrown in. The connection for the field is taken off 
the dynamo leads so that the opening of the main 
switch will not open the field circuit, and for this rea¬ 
son the field will begin to build up as soon as the 

































































170 


WIRING DIAGRAMS 


machine is started. Pilot lamps are sometimes used 
in place of voltmeter V, the voltage being determined 
by the brightness of the lamp. This is a very un¬ 
satisfactory method and is very little used at the 
present time. If either the armature or field connec¬ 
tions are reversed current will flow in the opposite 
direction. 



Figure 141 shows the connections of a compound- 
wound dynamo. This machine, like the shunt-wound 
machine, is used where a current of constant poten¬ 
tial is desired, but it has the advantage over the shunt 
machine in that it maintains the voltage more con¬ 
stant over a greater variation in load. The winding 
varies from that of the shunt dynamo in having, in 
addition to the shunt field, an auxiliary field which 
is in series with the armature. It is in reality the 
winding of both the shunt and series machine on one 
























































DIRECT CURRENT GENERATORS 171 


machine. A? the current supplied by the dynamo 
increases, the current in the series field winding in¬ 
creases, thus increasing the field magnetism and the 
voltage. In this way the voltage is kept practically 
constant. 

When a dynamo of this kind is used to supply a 
large load located at some distance from the gen¬ 
erator, it is sometimes desirable to have the voltage at 
the dynamo terminals increase as the load increases, 
to overcome the increased drop in the line due to the 
losses from increased current. To accomplish this a 
method known as over-compounding is used, the series 
windings being so calculated that, as the current in¬ 
creases, the voltage will rise accordingly. 

In some cases the shunt field is connected between 
one brush and the end of the series winding, as shown 
in the dotted lines. This is known as the long shunt, 
the method of connecting directly across the brushes 
being known as the short shunt. A rheostat R is 
connected in the shunt field and serves the same pur¬ 
pose as in the shunt machine. 

Figure 142 shows the connections when two shunt- 
wound machines are to be run in parallel. The wind¬ 
ing of these machines is the same as shown in Figure 
140. The positive lead of each machine is connected 
to the same bus bar. In starting, if it is desired to 
use but one machine, the method described in Figure 
140 is followed. When one of the machines is running 
and the other is to be thrown in, the idle machimi 








172 


WIRING DIAGRAMS 


is brought up to speed with the main switch open and 
the voltage regulated by means of the; rheostat and 
voltmeter until the voltages of the two machines cor¬ 
respond. The main switch is then thrown in and the 
load on the two machines, which is ascertained by the 
ammeters, is equalized by means of the rheostats. If i 



machines, the higher one wull run the other as a motor 
without changing the direction of rotation. The field 
current will remain unchanged and the armature cur¬ 
rent of the low dynamo will be reversed, which w T ill 
cause it to run in the same direction as a motor as it 
ran as a dynamo. 





































































































DIRECT CURRENT GENERATORS 173 


When a plant feeding motors is shut down the 
switches on motors should first be opened, or very 
likely motor fuses will blow. As the voltage goes 
down the motors will draw more current to do the 
work. If a plant is shut down with the motor 
switches “on” it will generally be found impossible 
to start up a shunt dynamo, the low resistance in the 
mains not allowing enough current to flow around 
the shunt fields to energize them. 



FIGURE 143. 


Figure 143 shows connections for two compound- 
wound dynamos run in parallel, the winding of each 
machine being the same as in Figure 141. When two 
or more compound-wound dynamos are to be run to¬ 
gether, the series fields of all the machines are con- 



























































































V74 


WIRING DIAGRAMS 


nectcd together in parallel by means of wire leads 
or bus bars, which connect together the brushes from, 
which the series fields are taken. This is known as 
the equalizer, and is shown by the line running to 
the middle pole of the dynamo switch. By tracing 
out the series circuits it will be seen that the current 
from the upper brush of either dynamo has two paths 
to its bus bar. One of these leads through its own 
fields, and the other, by means of the equalizer bar, 
through the fields of the other dynamo. So long as 
both machines are generating equally there is no dif¬ 
ference of potential between the brushes of Nos. 1 and 
2. Should, from any cause, the voltage of one ma¬ 
chine be lowered, current from the other machine 
would begin to flow through its fields and thereby 
raise the voltage, at the same time reducing its own 
until both are again equal. 

The equalizer may never be called upon to carry 
much current, but to have the machines regulate 
closely it should be of very low resistance. It may 
also be run as shown by the dotted lines, but this will 
leave all the machines alive w r hen any one is generat¬ 
ing. The ammeters should be connected as shown. 
If they were on the other side they would come under 
the influence of the equalizing current and w r ould in¬ 
dicate wrong, either too high or too low. The equal¬ 
izer should be closed at the same time, or preferably 
a little before, the mains are closed. In some cases 
the middle, or equalizer, blade of the dynamo switch 


— 



DIRECT CURRENT GENERATORS 175 


is made longer than the outsides to accomplish this. 
The series fields are often regulated by a shunt of 
variable resistance. To insure the best results, com- 
pound-wound machines should be run at just the 
proper speed, otherwise the proportions between the 
shunt and series coils are disturbed. 



Figure 144 shows connections where two shunt- 
wound machines are connected to operate on what is 
known as the three-wire system. The two dynamos 
are connected in series, three wires being canied from 
them; one from the outside pole of each machine and 
one from the junction of the two machines. The 
voltage between these outside wires is equal to the 














































































































176 


WIRING DIAGRAMS 


combined voltage of the two machines, and the volt¬ 
age between the outside and the central or neutral 
wire is equal to the voltage of the corresponding ma¬ 
chine. If the load on both sides of the system is 
equal there will be no current flowing in the neutral 
wire, while if the loads are unequal the neutral wire 
will have to carry only the difference in currents be¬ 
tween the two outsides. 

The advantage derived from the use of the three- 
wire system lies in the fact that one wire (which 
would have to be used were the two machines operated 
on two separate circuits) can be done away with, and 
on account of the voltage being doubled the wires 
can be of much smaller capacity. For the same per 
cent of loss the amount of wire required to operate 
the three-wire system, when the neutral wire is of the 
same size as the outsides, is but three-eighths of that 
required with a two-wire system. This system is 
used to a great extent in the large cities for central 
station, direct current distribution, and it is also 
used on the secondary mains in alternating current 
work. 

In the feeder lines of the direct current system the 
neutral wire is generally made one-third the size of 
the outsides, while in the secondary mains in both 
direct and alternating current work all three wires 
are made of the same size; for, if one of the outside 
fuses should blow, the neutral would have to carry 
the full current. 


DIRECT CURRENT GENERATORS 177 


Figure 145 shows a diagram of the winding and 
connections of a Western Electric compound-wound 
compensator set. This apparatus is used in connec¬ 
tion with 220 volt generators and by means of it a 
three-wire 110-220 volt system is obtained. This set 
consists of two motors, the armatures of which are 
mounted on the same shaft so that both run at the 
same speed. When the machines are started the 
switch P and the circuit-breaker are left open and the 
switch shown at the left closed. The machines are 
then started by means of the starting box. Tracing 
out the circuits it will be seen that the main current 
from the positive pole of the switch passes through 
the starting box, through the armature and series 
fields of machine B then through the armature and 
series fields of machine A and back to the negative 
side of the line. The circuit for the shunt fields is 
connected to the starting box, current flowing through 
the resistance box, R, and then through the shunt 
fields of machine A and machine B, these fields being 
connected in series, to the negative side of the line. 
It will be noticed by the direction of the arrows that 
the current in the series fields and the shunt fields are 
in opposition. This remains so in both motors only 
while the load on both sides of the neutral is even 
and under this condition the amount of current in the 
series fields is very small. If an additional load is 
thrown on one side, say ten lamps at X, part of the 
excess current flows along the neutral wire to the 


WIRING DIAGRAMS 


V8 



FIGURE 145 







































































































COMPENSATORS 


179 


armature and series fields of machine A. This cur¬ 
rent being in opposition to the current in the shunt 
fields weakens them and tends to speed up this motor. 
This speeding up increases the counter E. M. F. of 
machine B, the fields of which have not been weak¬ 
ened, and current flows out of the armature and 
through the series fields in a direction opposite to that 
shown by the arrows. The current in both field coils 
in this machine will now be in the same direction and 
the machine will act as a compound-wound generator. 
It cannot as a generator give out more power than 
it receives from A as a motor and will generate a 
little less than one-half of the excess current used at 
X. This is shown a little plainer by the diagrams in 
Figure 146. With no load, or with the load evenly 
distributed on both sides of the neutral, the condi¬ 
tions will be as shown in the upper diagram, both 
machines acting as motors. With excess of load be¬ 
tween the positive and neutral approximately one- 
half of the excess current will pass along the neutral 
wire through the lower machine causing it to act as 
a motor while the balance of the excess current is sup¬ 
plied by the upper machine acting as a generator. 
The lower diagram shows the conditions with excess 
load between the neutral and the negative. In the 
operation of these machines, when they have attained 
full speed after starting, their voltages are equalized 
by means of the resistance box R, this box being 
placed in the strongest field. When automatic start- 


180 


WIRING DIAGRAMS 


ing boxes are used, as in this case, it is almost always 
necessary to place the resistance box in the opposite 
field to balance the resistance of the magnet on the 
starting box. For equalizing the voltages connec¬ 
tions are made to the voltmeter as shown in Figure 



143, so that reading for both machines can be taken. 
When the machines are at even voltage the circuit 
breakers are thrown in. 

Figure 147 shows the switchboard and machine 
connections for two Compensator sets in parallel. 
The two panels at the left are for the 220 volt gen-v 
erators, the two at the right are for the feeders while 



























COMPENSATORS 


181 


the two center panels are for the operation of the 
compensators. By following out the circuits for the 



individual compensators it will be seen that, with few 
exceptions, they correspond to the circuits shown in 


FIGURE W 








































































































































































































































182 


WIRING DIAGRAMS 


Figure 145. A resistance box is installed in each 
shunt field circuit while in Figure 145 there is only 
one resistance box. 

The principle of the Westinghouse Three Wire 
Generator is illustrated in Figures 147a, 147b, and 



147c. Figure 147a shows the connections of the 
dynamo armature. The outer circle represents the 
ordinary armature winding connected by means of the 
commutator to the brushes A and B. The fine coils 
shown running through the center from C to D repre¬ 
sent taps taken from diametrically opposite points 
of the direct current winding. If these taps are joined 
through resistances as indicated alternating currents 
will circulate in them and at E there will be a point at 
which just half of the voltage of the direct current 
system exists. The wire connected to this point can 
therefore be used to fulfill the same requirements as 
the neutral wire in the ordinary two generator three 
wire system. 

















ALTERNATING CURRENT GENERATOR 133 


The connections of a single machine are shown in 
Figure 147b. In actual practice the alternating cur¬ 
rent connections of the armature are connected to two 
auto transformers as shown. These auto transformers 
are known also as balancing coils. 

Figure 147c shows the switchboard connections for 
two such generators operating in multiple. On 



account of the fact that the load is often unbalanced an 
ammeter is provided in each leg leading from a ma¬ 
chine to the switchboard. The series fields of each 
machine are also divided so that current from each 
leg may pass through half of each field. Since the 



























































































184 


WIRING DIAGRAMS 


series fields are divided it is necessary to run an equal¬ 
izer for each division and two are therefore shown. 

The balancing coils should be mounted as near to 
the dynamos or switchboard as practicable. Any 
great resistance introduced into their circuit will affect 
the voltage existing between the neutral point and the 
outside wires. It should be noted that both the 
positive and negative equalizer connections as well as 
both the positive and negative leads are run to the cir¬ 



cuit breakers in addition to the main switches on the 
board. This is necessary in all cases. Otherwise, 
when twx) or more machines are running in parallel 
and the breaker comes out opening the circuit to one 
of them but not breaking its equalizer leads, its am- 










































































ALTERNATING CURRENT GENERATOR 185 


meter is left connected to the equalizer bus bars and 
current is fed into it from the other machines through 
the equalizer bars either driving it as a motor or burn¬ 
ing out the armature. 

Once properly installed the balancing coils require 
no further attention and give no trouble. Provision 
should however be made so that their circuit cannot be 
opened accidentally while in operation. 



Figure 148 shows the connections of a single-phase, 
alternating current generator. The field of this ma¬ 
chine is excited by a direct current, part of which is 
taken from some outside source (generally a small 
dynamo belted to the shaft of the alternator) and 
part of which is taken from the windings of the al¬ 
ternator, the current being rectified by means of the 


















































186 


WIRING DIAGRAMS 


commutator C. This commutator has as many seg-* 
ments as there are poles to the dynamo, and the al¬ 
ternate segments are connected together as shown in 
the small diagram. S is a German silver resistance 
which is connected in shunt across this rectifying 
commutator. The main current coming from the 
armature is shunted, part going through the shunts, 
the remainder around the field winding. 

It will be seen that this method of field excitation 
is very similar to that used on the compound-wound 
direct-current dynamo. In the diagram shown both 



of the field windings encircle every pole, but in some 
machines the rectified current will traverse a few 
poles only, the current from separate exciter travers¬ 
ing the remainder. Current on these machines is 
usually generated at high voltage, and transformers 
are used at the point of supply to cut the voltage 
down to that required. The transformer T is used 











ALTERNATING CURRENT GENERATOR 187 


in connection with voltmeter V to reduce the voltage 
on that instrument. 

Figure 148a shows a theoretical diagram of a mono- 
cyclic generator of the General Electric Co. Such 
generators are sometimes used on systems where the 
lighting load is the main factor and only a few self 
starting motors are to be operated. It is essentially 
a single phase alternator with an extra winding of 
smaller capacity placed so as to produce a phase dif¬ 
ference of 90 degrees between the currents in the main 
coil and those in the smaller. The smaller winding is 
known as a “teazer” coil, and the middle wire to which 
this coil attaches is spoken of as the “teazer” wire. 
The machine carries three collector rings. The 
arrangement of the wires placed upon the armature can 
be seen from the figure at the right. The main coils 
are placed in the deep slots and the teazer coils into 
the shallow ones. 

In the General Electric generator, if the voltage 
between the two main wires is 2080 there will be 
difference of potential between either of the outsides 
and the teazer of 1160. 

The field connections of a monocyclic generator are 
shown in Figure 148b, and the diagram is self explan¬ 
atory. 

The armature connections are given in Figure 148c, 
and the following instructions are quoted from the 
General Electric Co. “The armature of a standard 
monocyclic generator rotates in the counter-clockwise 


To ETx crLer- 


\ss 


WIRING DIAGRAMS 


CONNECTIONS OF MONOCYCLIC GENERATOR 



For 2300 Volt Generators, connect as shown by solid lines. 
For 1150 Volt Generators, omit connections A to B, C to D, 
E to F, and G- to H, and connect as shown by dotted lines. 


FIGURE 148b. 


To Cxcit-er 




































































ALTERNATING CURRENT GENERATOR 189 


direction as one faces the commutator. When the 
generator is loaded, the voltage between the teazer 
coil and the two terminals of the main coil may be 
different; therefore, it is necessary to have the com. 
mutator connected in corresponding ends of the main 
coil. 

“ If the machine has not been arranged for clockwise 
rotation the following change in the connections on the 
commutator-collector must be made if the machine is 



to be run in parallel with another. The diagram 
Figure 148b shows the connections of monocylic gen¬ 
erators. In this diagram the studs on the commutator- 
collector marked 1 and 6 are the terminals of the main 
coil. These should be reversed. The numbers are 
stamped on the end of the stud and may be seen with 
the aid of a mirror. By referring to the diagram it is 
















To Exciter- 


190 WIRING DIAGRAMS 

CONNECTIONS OF THREE-PHASE GENERATOR 



Cor~r~» m i_it .a*-,or 
CONNECTIONS FOR SERIES FIELD 


For 2300 Volt Generators, connect as shown by solid lines. 
For 1150 Volt Generators, omit connections A to B, C to D, 
E to F, and G to H, and connect as shown by dotted lines. 


FIGURE 148d. 


To Excit/©r 




































































ALTERNATING CURRENT GENERATOR 191 


a simple matter to trace out the connections with the 
aid of a magneto, after the armature leads have been 
disconnected and the brushes raised.” 

Figure 148d shows the connections of a General 
Electric three phase generator. This machine, as well 
as all of the foregoing, is of the revolving armature 
type. Many of the larger machines are now built 
with stationary armatures and revolving fields. In 
such case the exciter feeds the moving element and the 
line currents are taken from the stationary windings. 

Two three phase composite wound generators are 
shown connected together for parallel running in 
Figure 148e. 

Composite wound alternators if used with inductive 
loads require considerable attention at the rectifier. 
A change in the angle of lag of the current behind the 
E. M. F. must be followed by a change in the adjust¬ 
ment of the rectifier or there will be much sparking. 
For this reason such machines are used mostly on 
lighting circuits only. 

Figure 148f gives the switchboard connections of 
two two phase machines arranged for parallel running. 
Each machine is equipped with a throwover switch 
by which either phase may be connected to voltmeter. 
Each phase is also equipped with an ammeter. 

E E are the rheostats by which the field strength 
of either machine can be adjusted. The synchron¬ 
izing bus S is equipped with a throwover switch so 
that the synchronizing may be either dark or bright. 


192 


WIRING DIAGRAMS 


Whichever method is preferred should be settled upon 
and the switch locked so that it may not be accidentally 
changed. Synchronizing lamps of double the voltage 
capacity of the system must be provided as the two 






































































































ALTERNATING CURRENT GENERATOR 193 


machines are likely to be in series during part of the 
time of synchronization. 

The instrument connections of a three phase 44(7 
Volt switchboard for parallel operation of two ma f 





































































































194 


WIRING DIAGRAMS 



FIGURE 148k, 







































































































































ALTERNATING CURRENT GENERATOR 195 


chines are given in Figure 148g. To avoid confusion 
the exciter circuits and those leading to lamps and 
motors are omitted. 

An ammeter is provided for eaeh machine by which 
it can be determined whether it is taking its share of 
the load. There is further an ammeter in each phase 
of the bus bars to indicate the balance maintained on 
the system. 

W is a recording watt meter; W' an indicating 
watt meter; P a power factor meter, and F a frequency 

toeter. (See Figure 154s.) 

L and L' are the synchronizing lamps, two of which 
are provided for each machine. To synchronize 
machine 2 with 1 which is already running, the plug is 
inserted as at S, the lower half of the plug closes gap 3 
and the upper half closes gap 4 through the lamps L. 
If the machines are not in synchronism the lamps will 
alternately be bright and dark. The speed of the in¬ 
coming machine must be altered until the periods of 
light and darkness are of several seconds duration. 
During the middle of the dark period the main switch 
may be closed and the machines will then operate 

together. 

By tracing out the circuits it can be seen that the 
plug placed as at S' by being inserted in the upper, 
middle, or lower set of contacts can be used to take 
the reading of either of the three phases on the volt¬ 
meter V. The voltmeter is also connected so as to be 
available as a ground detector. 



195a 


WIRING DIAGRAMS 




ARC LAMP CONTROL FOR MOTION PICTURE WORK 

Arc lamps used in connection with motion picture 
machines have caused the construction of some special 
forms of generators. 

Figure 148h shows the connections of an alternating- 
current to a direct-current motor-generator of the 
Fort Wayne Electric Company. The switch A is 
used to start it and is shown connected to a three- 
phase line. Aside from the field winding there are 
three wires leading to the generator. The wire B 
carries a compound winding inside of the generator 
which opposes the magnetization of the shunt wind¬ 
ing. The wire C carries another compound winding 
which is arranged to strengthen the shunt field. D 
is a box containing two resistances, one for each arc 
lamp shown. 

If only one lamp is to burn, the switch E is closed 
and the arc started in the usual way. When ready 
to change to the other arc lamp, switch E must be 
opened, the switch on the second arc lamp closed, and 
the arc struck. Then extinguish the first arc and 
close the switch E again. If both lamps are to be 
used continually, switch E must he left open. 

As long as current is used through wire B, there is 
no loss of energy in any resistance and should the 
current in the arc rise, as when the electrodes are 
brought together, the increased current in the series 
winding, cut into this wire, would weaken the 
field and thus keep the current down. When current 
is used through the wire C, the series field winding 
strengthens the field and builds up the voltage suf¬ 
ficiently so that the lamps may he operated through 
the resistances. The field strength mav be further 
regulated by the rheostat 7?. 














ALTERNATING CURRENT GENERATOR 195b 


Another connection of the Fort Wayne motor-gen¬ 
erator h shown in Figure 148i. In this case the lamps 
may be operated either from the compensarc C or the 
generator. By throwing either one of the switches 
connected to the arc lamps up, the corresponding 
arc lamp is connected to the compensarc. By throw¬ 
ing the switch down it is fed from the generator. 
The lamp, by which the picture is being projected, 
should be fed from the generator and when nearly 



ready to change, the other may be started on the 
compensarc. This lamp will burn with a short arc 
and when it is connected in parallel with the one on 
the generator, it will immediately extinguish the lat¬ 
ter. 

Another combination of motor and generator some¬ 
times used is shown in Figure 148j. By tracing out 
the circuits it will be seen that the armatures of both 
are in series and that the electrodes, when they come 






















































195c 


WIRING DIAGRAMS 


together, form a shunt about B. With the electrodes 
separated, if current is turned on, it must pass 
through both armatures in series. Thus the counter 
e.m.f. of both armatures opposes that of the line and 
they operate at a certain speed. Each motor has a 
natural tendency to send current in opposition to that 
impressed upon it by the line. If then the electrodes 
are brought together, they at once form a short cir¬ 
cuit around the armature of B. The current in B 





FIGURE 148i. 


reverses and it then begins to act as a generator and 
sends current through the arc lamp. The current 
which passes through the armature of A also passes 
through the arc lamp. A is then a motor and oper¬ 
ates B as a generator. 

The voltage at the arc is less than the line voltage 
by as much as the counter e.m.f. of motor A amounts 
to, neglecting the drop in voltage due to resistance. 
No resistance is needed if the winding is properly 
arranged and there is not the loss in heat which goes 
with the use of resistances. This arrangement can 
be used with direct-current circuits only. It is not 
suitable where the supply voltage is very much higher 






























































ALTERNATING CURRENT GENERATOR 195d 


than the voltage used at the arc. A field rheostat is 
provided to adjust the field strength of B. A is 
equipped with the ordinary motor-starting rheostat 
only. 

Rotary Converter Control .—This is a machine used 
only where the supply is alternating current. The 
voltage delivered to the converter must be the same 
as that desired at the direct-current terminals. This 
machine has an armature essentially similar to that 
of a direct-current dynamo. Alternating current is 
supplied to it at one set of terminals and direct cur- 



as motor and generator at the same time. Whatever 
voltage regulating is necessary with this machine must 
be done on the alternating-current side. Changing 
the field strength does not materially affect the volt¬ 
age so that no means for regulating the fieid stiength 

is provided. 

The polarity of the direct-current terminals de¬ 
pends upon the position the armature happens to be 
in when the alternating current is applied to it and is 
very apt to come in wrong when the machine is 
started. It is therefore necessary to have a polarity 
indicating voltmeter in the circuit and to watch it 
when starting the machine. If the polarity is wrong, 
























































195e 


WIRING DIAGRAMS 


the switch must be opened and in a moment thrown 
in again; and if still wrong, this process must be re¬ 
peated until the polarity comes right. Each arc lamp 
fed from a converter must be equipped with re¬ 
sistance. 



The Martin rotary converter is especially designed 
for motion-picture work and may be provided with 
the proper connections for either single-phase, two^ 















































































































































ALTERNATING CURRENT GENERATOR 195f 


phase, or three-phase work. There is a stator ring 
which entirely surrounds the armature. This ring is 
made up of laminated disks with squirrel-cage bars 
and slots alternating. The squirrel-cage bars are 
joined at the end to a copper bar and it is by the aid 
of this squirrel-cage that the motor may be started 
and brought into step. The squirrel-cage also pre¬ 
vents “ hunting ” which is one of the common 
troubles experienced with synchronous motors or con¬ 
verters. Into the slots are wound special compen¬ 
sating coils to balance the armature reaction and 
keep the neutral point in constant position from no 
load to full load. This prevents sparking at the 
brushes. On the outside of this damper ring or 
squirrel-cage winding is the regular shunt-field wind¬ 
ing used with direct-current motors or generators. 

Figure 148k is a diagram showing the connections 
of the Martin Rotary Converter as installed by the 
Northwestern Electric Company of Chicago. This 
switchboard is equipped to operate two moving-pic¬ 
ture arcs, two dissolving stereopticon lamps, and one 
spot light. Each lamp is provided with a throw-over 
switch so that current may be used, either from the 
alternating-current mains direct or from the direct- 
current side of the converter. 

Figure 1481 is another panel hoard for moving- 
picture work made up by the same company. In this 
case resistances are provided for use when the arc 
lamps are operated from the converter. In case it 
is desired to run from the alternating-current mains, 
transformers or compensarcs are used. The emer¬ 
gency feature of these panel boards is highly to be 
recommended. It must be borne in mind that one 
may suddenly be forced to deal with an operator who 


195g 


WIRING DIAGRAMS 


has never seen a converter and knows nothing of its 
operation; and there is also always the possibility of 
some trouble with the machine. 



A Martin rotary converter to be operated from a 
single-phase line is shown in Figure 148m. This ma¬ 
chine is started through the commutator side, in 

































































































































ALTERNATING CURRENT GENERATOR 1951 


order to start this machine it is necessary first to 
close the main switch. Next throw the switch 2 to the 
right and leave it there for about five seconds. It 
may then be thrown over to the running position at 
the left and allowed to remain in this position. If 



the polarity is not correct, the switch must be opened 
again for an instant and closed again; and this pro¬ 
cess must be repeated until the polarity comes in 
right. To stop the converter, first open the main 
switch and then the throw-over switch. 























































CHAPTER XV. 


ALTERNATING CURRENT MOTORS. TRANSFORMERS. 

There are two general classes of alternating-cur¬ 
rent motors, known respectively as “synchronous” 
and “induction” motors. As an example of the first 
class: If two identical alternating-current dynamos 
are connected together by wires, one running as a 
generator and the other as a motor, the driven ma¬ 
chine would run at the same speed as the driving 
machine; for, at every change in the direction and 
strength of the current given out by the generator, 
like changes would be produced in the machine run¬ 
ning as a motor. They would then run in synchron¬ 
ism. It may be advisable to state here that the ma¬ 
chine running as a motor would first have to be 
brought up to speed, as the majority of synchronous 
motors are not self-starting. 

When a multiphase (2 or 3-phase) alternating cur¬ 
rent is sent around the fields of an alternating cur¬ 
rent motor, a revolving field is set up in the space 
occupied by the armature. If now an armature of 
what is known as the squirrel cage type (a laminated 
armature in which bars of copper, running parallel 
to the shaft, are imbedded in slots in the periphery, 
the ends of all the bars being connected together, 

19f> 


ALTERNATING CURRENT MOTORS 197 


(Figure 149), is placed in this field, currents 
will bo induced in it which, acting in conjunc¬ 
tion with the revolving field, will cause the armature 
to turn. These are known as induction motors, and 
this class is generally employed in commercial work. 
Such motors will start themselves from rest with a 
considerable torque, and will stand a reasonable 
amount of overload. 

The direction of rotation of motors of this kind 
is reversed by changing the relative position of wires 
in any phase. It can readily be seen that this will 
cause the revolving field to move in the opposite di¬ 
rection. 



FIGURE 149. 


The action of the current in the starting of in¬ 
duction motors is very similar to that in direct-cur¬ 
rent motors in that if, while the motor is at rest, the 
current was thrown directly on, it would rise to a 
considerable value. The smaller size motors may be 
directly connected to the circuit as is often done with 
direct current motors but with the larger size motors 
>ome device must be used to keep down the excessive 
current on starting. 







198 


WIRING DIAGRAMS 


Resistance boxes may be inserted in tbe motor cir¬ 
cuits and operated in the same way as on direct cur¬ 
rent apparatus the resistance reducing the voltage at 
the motor terminals. On two and three-phase work 
resistances must be inserted in each phase and ar¬ 
ranged to work together so that the changes in pres¬ 
sure at the motor terminals will be the same. 



Figure 150 shows the connections of the General 
Electric Company’s compensator used in starting 
three-phase motors. This apparatus consists of three 
coils wound on laminated iron cores forming an auto¬ 
transformer in which one wire is used for both pri¬ 
mary and secondary, and works on the principle that, 
if an alternate current is sent through a coil of 
wire, and a tap taken from some intermediate point 
in the winding, the voltage between the tap and the 
end of the coil will be less than the full voltage sup* 



















































ALTERNATING CURRENT MOTORS 199 


plied, depending on the position at which the tap is 
taken off. In the diagram suppose that the differ¬ 
ence of potential between the terminals A and B were 
115 volts; then the difference of potential between A 
and 4 would be less than 115, while the difference of 
potential betw een A and 3 would be less than between 
A and 4. To start the motor the switch is thrown to 
the lower position, when the motor will receive the 
reduced current due to the reduced voltage between 
A and 4. When the motor is up to speed the swutch 
is thrown to the “up” position, when the motor will 
receive the full voltage of the line. If more current 
is required in starting than can be obtained with the 
connection at 1 (this being the point of lowest volt¬ 
age), connection can be made at either 2, S or 4 
until the current required to start the motor is ob¬ 
tained. Were the motor, while at rest, thrown di¬ 
rectly onto the mains without the use of the com¬ 
pensator, the current would rise to six or seven times 
that normally required; w r hile in starting with the 
compensator the current varies from full load to 
about twuce full load current according to whether 
connection is made at 1 or 4. 

Another method used in starting alternating cur¬ 
rent motors is shown by the diagrams in Figure 151. 
The upper diagram shows the connections on a three- 
phase armature where one end of each coil is connected 
to a common wire, the other ends of the coils being 
carried to contact shoes Bo? ween the contact 


200 


WIRING DIAGRAMS 


shoes 2, 2 9 2 and 1, 1 9 1 are connected resistance 
wires, these wires ending in a connection common to 
them all. When the motor is started current flow¬ 
ing from the armature coils passes through the re¬ 
resistances r and s . This is shown in the lower left 
hand diagram. 4s the motor speeds up the contact 





shoes 1,1,1 are short-circuited, thus short-circuiting 
the resistances r, V, r as shown in the middle diagram. 
As the speed further increases the contact shoes 2, 
2, 2 are short-circuited, this in turn short-circuiting 
the resistances s , s> s. The motor will now run with 
no resistance in the armature circuit as shown in th« 
diagram at the right. 



ALTERNATING CURRENT MOTORS 201 


Figure 152 shows the connections for the Wagner 
single-phase alternating-current motor. On top of 
the motor are three binding posts. Posts 1 and 3 
are connected to the terminals of the field winding* 




while post 2 is connected to an intermediate point be¬ 
tween 1 and 3. When the motor is called upon to 
start a heavy load, the double-throw switch shown in 
the lower diagram is used. With the switch thrown 
to the upper position connection is made to posts 1 


































202 


WIRING DIAGRAMS 


and 2, when, on account of part of the field winding 
being cut out, a greater amount of current is sent 
through the fields and the torque increased. When 
the motor is up to speed the switch is thrown to the 
lower position, where current will be sent through 
the entire field winding. 

The armature winding consists of a number of 
copper bars terminating in a commutator at one end. 
While running up to speed the armature is short- 
circuited through brushes which bear on the commu¬ 
tator and produce in the armature poles which, act¬ 
ing with the fields, cause the armature to revolve. 
On attaining full speed an automatic governor 
mounted on the shaft lifts the brushes off the com¬ 
mutator, and at the same time short-circuits all the 
commutator bars. The motor now runs as an induc¬ 
tion motor. The upper connections are used where 
an ordinary load is to be started. 

This motor is reversed by moving the brushes on 
the commutator. Note the markings on the brush 
holder. The starting torque can also be varied by 
shifting the brushes. It will be greater as the mark 
on the brush holder is moved farther from the center 
mark. 

Single-phase motors, unlike the multiphase motors, 
will not start themselves from rest without the provi¬ 
sion of some special means. A number of different 
methods are in use to make these motors self-starting, 
(n the small fan motors made by the General Electric 


ALTERNATING CURRENT MOTORS 203 


Co. the ends of the pole pieces are slotted, and around 
one of the projecting ends is placed a band of cop¬ 
per (Figure 153). The effect of this band of cop¬ 
per is to cause two magnetic fields under each pole 
piece, one being slightly out of step with the other. 
This has an effect on the armature similar to a two- 
phase current, and causes it to revolve. 



FIGURE 153. 


Another method, known as the “split phase,” is 
used for the same purpose. In some of the smaller 
motors made by the Holtzer-Cabot Co. the field is 
wound with two separate coils, one having a few 
turns of comparatively large wire and the other a 
great number of turns of fine wire. When current 
is turned on, owing to the difference in self-induction 
of the two coils, a field similar to the two-phase field 
is set up and the armature caused to revolve. When 
the motor has reached synchronism, the current to 
the high resistance coil is opened and the motor op¬ 
erated on the low resistance coil alone. 




204 


WIRING DIAGRAMS 


Other methods of bringing single-phase motors up 
Jo speed are described in Figures 154 and 152. Any 
small direct-current series motor can be used on al¬ 
ternating current providing the field magnets are 
laminated. The larger motors generally contain too 
much self-induction to be operated on alternating 
current. 



FIGURE 154. 


Figure 154 shows the connections of the Fort 
Wayne alternating-current, single-phase motor. In 
order to start this motor and bring it up to speed. 


























































ALTERNATING CURRENT MOTORS 205 


the armature is provided with an extra winding con¬ 
nected to the commutator C, shown at the left. When 
the motor is to be started, the switch S, which is 
hinged at N, N r , is closed to the left. Current from 
the left-hand main will then pass through the contacts 
N', M', on the switch S to the series winding, and 
then to the commutator and armature and out through 
M, N, on switch, to other side of line. At each re¬ 
versal of the current the magnetism in both fields 
and armature is reversed at the same time, thus caus¬ 
ing a steady pull in one direction on the armature. 

As the motor comes to speed the pilot lamp P will 
gradually light up, and when it has reached full 
candlepower the switch S is thrown to the right. Cur¬ 
rent from the left-hand main will now pass through 
contacts N', T', on switch, to the collector rings, 
through the armature, and out through points T, N, 
on switch to other side of line. At the same time 
tb? contacts V, V' and W, W' on switch S will be 
short-circuited (these points of the switch are not 
in electrical connection with the blades, being sep¬ 
arated therefrom by an insulator, as shown in figure 
in upper right-hand corner), and the shunt field cir¬ 
cuit closed through the commutator; the direct cur¬ 
rent from the commutator passing from the lower 
brush through the points V, V', on switch, to the 
shunt field and back to points W, W', and through 
the rheostat R to the upper brush on commutator. 
The motor will now run as a synchronous motor, the 


206 


WIRING DIAGRAMS 


armature receiving current from the mains, while the 
field is energized by means of the direct current 
generated in the extra winding in connection with 
commutator C. When the motor is running with the 
switch to the right the series field is open. 



Figure 154a shows theoretical diagram of what is 
termed the cascade or tandem method of coupling 
induction motors for variable speeds. The rotors of 
the two motors are mounted on the same shaft or in 
other manner mechanically coupled together. The 
main current from the generator feeds stator S of 1. 
The currents induced in the rotor R of 1 traverse the 
stator of 2 and the controlling resistance is cut into 
the rotor circuit of 2 as shown. 

The number of poles on two such machines may be 
so arranged that different changes in speed are possible. 
It is also possible to arrange switches so that the 





























































TRANSFORMERS 


207 


motors may be operated in parallel or No. 1 alone as 
shown. 

Figure 154b shows method of operating rolling mills 
or other devices that require a large amount of power 
for a very short time. The large induction motor I 



FIGURE 154b. 


is supplied by a limited amount of current from the 
mains. The amount of current that may be drawn 
from the mains is governed by an automatically con¬ 
trolled resistance placed in the rotor circuit. When¬ 
ever the main current rises above a predetermined 
value the core of the solenoid is drawn up and resist¬ 
ance is cut into the rotor circuit, thus keeping the main 
current in bounds. 

On the same shaft with the induction motor is a 
heavy balance wheel operating at a high speed and also 
the armature of a direct current generator. This 
generator carries a double wound armature which 











































































208 


WIRING DIAGRAMS 


feeds two motors connected to the shaft of the rolling 
mill. 

The only method of reversing and controlling the 
speed of the motors consists in changing the field 
strength of the generator. The fields of the generator 
are separately excited and controlled by resistances 
arranged similar to those of the well known Wheat¬ 
stone bridge. With the arm in the position shown 
no current is passing through the fields. If the arm 
is moved in the direction of the arrow the polarity of 
the fields will be as indicated, and when the arm 
assumes the position indicated by broken line the 
current strength will be at its maximum. If it is moved 
in the opposite direction the current in the generator 
fields will be reversed. 

The motors are also independently excited and the 
direction in which they move depends upon the direc¬ 
tion of the armature current, which in turn is governed 
by the current through the fields. With this arrange¬ 
ment it is possible to draw 4000 or 5000 H. P. for a 
short time without overloading the 1000 H. P. in¬ 
duction motor. 

Very small alternating current motors are usually 
connected to the line direct, and only a switch suited 
to the system is used. This switch does not even 
require to break all of the wires of the system. 

As the starting current of most alternating current 
motors is, however, much greater than the running 
current {especially if the motor start under load) it is 


TRANSFORMERS 


209 


advisable to place the motor under the protection of 
two sets of fuses. One such set of fuses is placed 
where the branch circuit is tapped off the mains, and 
the other at the motor switch. 

The manner of connecting a throwover switch to 
two and three phase motors so as to accomplish the 
desired result is shown in Figures 154c and 154d. 





6 


6 


6 



FIGURE 154c. 



The black circles represent the centers of the switch. 
Thrown upward the motor feeds direct from the mains 
which are fused to the starting current of the motor. 
After the motor has acquired its proper speed the 
switch is thrown downward and the motor feeds 
through the smaller fuses shown. 

In order to guard against leaving the motor without 
the proper fuse protection such switches are some¬ 
times equipped with springs which will not allow the 
switch to remain on the upper contacts. 



























210 


WIRING DIAGRAMS 



Throwover switches for the starting of motors in 
connection with auto transformers or compensators 
are shown in Figures 154e and 154f. 

To start, the switch is thrown to the right; this 
forces the current to pass through the transformers 
and reduces the voltage at the motor. After the motor 
has attained some speed the switch is thrown to the 



FIGURE 154g. 































































































TRANSFORMERS 


211 



left and connects the motor to the mains. The start¬ 
ing torque of the motor may be increased by connect¬ 
ing the taps leading from the transformers so as to 
leave less of their reactance in the circuit. 

The connections of General Electric controllers for 
three phase; two phase four wire and two phase three 
wire are shown respectively in Figures 154g, 154h, 
and 154i. The contact points on the drums in the 
center make connections either to the upper or lower 



FIGURE 154L 




































































































212 


WIRING DIAGRAMS 


connections shown. The motor leads are connected 
to the drum. Thrown downward the current must 
pass through the auto transformers which reduces the 
voltage. Thrown upward the motor is connected 
direct to the mains. 

^ Figure 154j shows diagram of a three phase auto 



FIGURE 154j. 


starter ^ith over and under load release as made by 
the General Electric Co. In order that the starter 
may remain in circuit there must be current in coil 1. 
Consequently when the voltage fails the starter opens 
the circuit. In case the motor is taking too much cur¬ 
rent one of the coils 2 or 3 opens the circuit through 1, 
and trips the starter thus opening the circuit. 

































































TRANSFORMERS 


213 


A similar arrangement is shown in Figure 154k, 
but is designed for high voltages and a voltage trans¬ 
former is provided as shown. 

With large motors the wiring is arranged as in Figure 

1541. 



For motors that start under light load and reo^i/e 
finer gradations in speed a controller as diagramatically 
shown in Figure 154m is often used. The compensator 
coils are inserted in two phases only; this results in 
unbalancing of the line but as long as the load is light 
this is not very objectionable. 

The speed of a three phase motor is considerably 
higher when its stator is connected in “mesh” or 




















































































214 


WIRING DIAGRAMS 


F 




Taps 


rr 


Tr/p Coi/S 

/fanning J 'ic/e 


To Mo Cor 


-Sconcing Side 



Compcnsoc o r 
MoonrC/z/no 
Sry/Cc/? 


o _ 


Conorc c/on Soor-d 
on CompcnsaCor 


FIGURE 1541. 


“delta” than when connected in Y or star. In Figure 
154n the throwover switch at the left is provided to 
change the winding from one to the other when re¬ 
quired. Thrown to the left the motor windings be¬ 
come star; thrown to the right they are delta. Motors 
must not be changed from star to delta unless it is 
known they are capable of running that way. 

A method of obtaining reduced voltage for the 
starting of three phase motors direct from trans¬ 
formers is given in Figure 154n. Thrown one way 
the motor obtains the full voltage of the line, and 
thrown the other way only about one half 





































TRANSFORMERS 


215 




FIGURE 154n. 



FIGURE 154o< 













































































































































































216 


WIRING DIAGRAMS 


Two and three phase motors are often equipped with 
wound armatures or rotors. In such cases the starting 
can be controlled by resistances placed in the rotor 
circuit about in the same way that it is placed in the 
armature circuit of direct current motors. Such 
resistances are also made variable and are illustrated 
in Figure 154p for three phase and Figure 154q for 
two phase. 




The rotor of an induction motor acts like the second¬ 
ary winding of a transformer, but as the rotor comes 
up to its proper speed the currents in it are much 
reduced. 

Small and medium size motors are sometimes con¬ 
nected to three phase systems as shown in Figure 154r. 
This is known as the open delta method. Only two 
transformers are required whereas to get the full three 
phase connection three would be necessary. 

Figure 154s shows the diagram of an automatic 
controller for three phase motor as made by Cutler 
Hammer, Co. The controller is operated by a single 
pole switch placed as at P, or, if the circuit be perma¬ 
nently closed at this point, closing of the main switch 

































TRANSFORMERS 


217 



FIGURE 154r. 


will automatically start the motor. 1, 2, 3 and 4 are 
solenoids which when energized draw up their cores 
and close the circuits indicated underneath. 

Solenoid 1 simply closes the phase wires A and B 
and thereby gives current to the stator windings of the 
motor M. 2, 3, and 4 when energized short circuit 
certain parts of the resistance R which is inserted in 
the rotor circuit. The three small solenoids 5 must 
be conceived as attached to the extremity of R at 5'; 
6 is attached to 6' and 7 and 8 at corresponding points 
of R, but only when the solenoids shown above them 
act. The solenoids are supposed to act in quick suc¬ 
cession in the order 1, 2, 3, 4; 4 when it acts finally 
short circuits the rotor at 8 r cutting all of R out. 

The operation is as follows: By closing the pilot 
switch P circuit is established from phase wire A 
through solenoid 1 line C point D pilot switch and phase 
wire B. There is also a parallel circuit through X. 
Thus energizing 1 causes its core to be drawn up; this 
closes the stator circuit of the motor and also the fine 
wire circuit at E. Current in the stator at once m- 



















218 


WIRING DIAGRAMS 


duces currents in the rotor and these draw up the cores 
of 5 opening the circuit underneath until the rotor has 
attained some speed. As the rotor attains speed the 
currents in it grow weaker and the cores of 5 drop back 
closing the circuit underneath again. 



FIGURE 154fl. 























































































































































TRANSFORMERS 


219 


As the circuit is now closed at E and underneath 5, 
current passes from phase A through solenoid 2 to E 
point D and thence to pilot switch and phase B. This 
causes 2 to draw up its core and the rotor resistance 
becomes short circuited at 6'. The small solenoids 
act as those at 5 momentarily opening the circuit and 
then closing it again. Drawing up the core of 2 closes 
the circuit at the left of G and opens that at the right. 
Current now passes from the left of 2 to the right of 
solenoid 3 thence to G and phase wire B at 1. Line 
C is now open and current passes from 1 through X 
to the pilot switch. This reduces the current leaving 
only as much as is necessary to maintain the core of 1 
against gravity. 

Solenoid 3 now acts closing the circuit at the left 
of H and under 7. This sends current from point X 
through solenoid 4 to the left half of H point D and 
pilot switch. 

When solenoid 4 acts it short circuits all of the resist¬ 
ance of the rotor and develops the full power of the 
motor. In its action it also closes the circuit of F at 
the left and opens it at the right. Closing the circuit 
F at the left establishes a circuit for 4 to point D, and 
at the same time opening of F at the right breaks the 
circuit of 2, and this core descending breaks the circuit 
of 3 at the left of G. Two circuits now remain closed, 
one through solenoid 1 resistance X to point D, the 
other around 2 and 3 to 4 left side of F and point D 
thence to Dil° f switch °nd phase B. 


220 


WIRING DIAGRAMS 


By tracing out the various circuits it can be seen 
that the arrangement is such that solenoid 2 cannot 
act unless 3 and 4 are in the off position and that 3 
cannot work unless 2 has acted and 4 must in turn 
wait on 3. The motor can therefore not be started 
unless all of the resistance is inserted in the rotor 
circuit. 

In Figure 154t a motor testing board suitable for 
ise with two or three phase currents is shown. The 



current in each phase may be measured and thus the 
degree of unbalancing of the circuit on individual 
motors determined. In practice it is found that very 
many motors are considerably out of balance elec¬ 
trically. 

The ammeter A is shown in connection with the 
wattmeter so that the power factor of the motor may 
be determined. The power factor is found by dividing 










































TRANSFORMERS 


221 


the indicated watts of the wattmeter by the product 
of the volts and amperes existing at the same time. 
The power factor is always less than unity. 

The switches indicated are all single pole with ex¬ 
ception of the voltmeter switch V. If 1, 4 and 7 are 
thrown upward the motor feeds direct from the line 
ABC. 

To test A for current throw 5 and 6 up and open 7; 
to get voltage A C throw V to right and 2 down. 



To test B for current throw 3 up, 5 and 6 down, and 
2 up, and open 4; to get voltage A B throw V to right. 

To test C for current throw 2, 6, 5, and 3 down and 
open 1. to get voltage C B throw "V to the left. 

There is often considerable trouble on three phase 
circuits from an unbalanced load, bor the best ser-» 
vice the current in all three wires should be the same. 
A simple method by which any one of the branch 
circuits may be transferred to any one of the phases 
is illustrated in Figure 154u. As shown each branch 
circuit is connected to a different phase. 
























222 


WIRING DIAGRAMS 


In Figure 154v the connections of the Westinghouse 
frequency meter are shown. The frequency meter is 
simply a voltmeter with two opposing coils acting 
upon the pointer. Placed in the circuit this way there 
would be no indications. 

In order to make it indicate different frequencies an 
inductive resistance is placed in circuit with one of the 



FIGURE 154v. 


coils and a non inductive resistance with the other. 
These resistances are placed in a separate case and 
mounted near the instrument to which they must be 
connected as shown. The frequency meter in any 
given case is of course simply a speed indicator since 
the frequency of the dynamos depends upon the speed 
with which they revolve. 

The connections of the Westinghouse portable 
poweriactor meter are shown for three phase circuit 
in Figure 154w and for two phase in Figure 154x. 















TRANSFORMERS 


223 


The two phase meter has two and the three phase 
meter three coils which form the fields. In addition 
there is another coil the currents of which are in phase 
with the voltage. A rotating field is produced by the 
main coils, and this field controls the position of the 
pointer attached to the movable coil. The connections 



to the movable coil are shown at the top and the 
arrangement for two phase is shown in center. 

The following instructions are quoted from publi¬ 
cations of the Westinghouse Company: “When the 
top binding posts are disconnected and there is current 
of at least one half full load in the series transformers, 
the pointer should rotate in the * lead direction, 
(f it rotates in the Tag’ direction reverse the leads 
running to the lower left hand binding posts. On a 
two phase circuit the reversal should be made at the 
series transformer shown at the left of the diagram. 
On a three phase circuit the leads should be reversed 
at the meter by connecting the common wire from the 














































224 


WIRING DIAGRAMS 


two series transformers to the left hand binding post, 
and the single wire from the series transformer on the 
left to the middle post. Then connect the shunt 
circuit to the upper binding posts as showm. This 
shunt connection should be made to the phase which 
is connected through the series transformer to the right 
hand side of the meter. Should it be necessary to 
reverse the series connection of the meter on three 
phase circuits from that shown on the diagram in 
order to obtain proper rotation, the shunt wire which 
is shown connected to the wire of the circuit having 
no series transformer should be changed to the wire 
which is connected through the series transformer to 
the left hand side of the meter. The upper half of 
the scale indicates for power delivered from alternating- 
current lines to the motor or rotary, and the lower half, 
power returned to the lines. Should the pointer indi¬ 
cate the reverse of that given above, the connections 
at the upper binding posts should be reversed. 

“Move the scale by means of the projecting studs at 
the sides of the dial, until the ‘frequency index’ at 
the lower right hand portion of the scale points to the 
line marked with the number of alternations of the 
circuit on which the instrument is being used. The 
instrument will now indicate the power factor of the 
circuit.” 

Figure 154y shows the ordinary connections of 
Westinghouse synchroscopes for voltages between 
1 and 200. 


TRANSFORMERS 


225 



FIGURE 154y. 



FIGURE 154z. 



FIGURE 154'. 


\ 

















































































































226 


WIRING DIAGRAMS 


The connections for voltages from 200 to 500 are 
given in Figure 154z and those for voltages in excess 
of 500 in Figure 154'. 


TRANSFORMERS. 

Figure 155 shows the circuits in a single-phase 
transformer. 

Figure 156 shows the circuits in a single-phase 
transformer with a three-wire secondary. This 
transformer has the advantages derived from the use 



FIGURE 155. FIGURE 156. FIGURE 157. 


of three-wire distributing circuits, and is used where 
a large installation is to be connected, or where one 
large transformer feeds a set of secondary mains sup¬ 
plying a number of residences. 

Figure 157 shows the connections of a two-phase 
transformer with two separate secondaries; and Fig¬ 
ure 158 the two-phase transformer with a common 
return wire for the secondaries. 


U! 












TRANSFORMERS 


227 


Figure 159 shows a three-phase delta connection, 
and Figure 160 a three-phase star connection. 

Figures 161 to 167 show the connections used on 
the Packard Mark VI. transformers. The primary 
windings of these transformers are made in two seQr 



FIGURE 158. 



FIGURE 159. 



tions, with leads brought out so that they may be 
connected either in series or parallel. When used on 

2000 volt systems the two sections are connected in 



series, and when used on 1000 volt systems the two 
sections are connected in parallel. These connections 
are showr in the diagrams, where, in Figures 161 to 


































































228 


WIRING DIAGRAMS 


164, terminal blocks are used, and in Figures 165 
and 168 the primaries are connected in the same way 
as the secondaries. The secondaries of these trans¬ 
formers are also wound in two sections, the same as 
the primaries, so that either 50 or 100 volts or 100 
or 200 volts may be obtained, according to the type 
of the transformer used. In Figures 161, 162, 165, 
166, the primary windings are connected in multiple; 
while in Figures 163, 164, 167, 168, the primary 



windings are connected in series. The two secondary 
windings are connected in series in Figures 161, 163, 
165, 167, and in multiple in Figures, 162, 164, 166. 
168. 

When a current of electricity is sent through a 
wire lines of force are sent out completely encircling 
the w T ire. As long as the current in the wire remains 
constant these lines of force remain constant, but, if 
the current increases the lines of force increase, or 












































TRANSFORMERS 


229 


if the current decreases the lines of force decrease. 
If the wire is wound into a coil as the current in the 
wire increases the lines of force sent out from each 
wire of the coil will have to cut through all the other 
wires on the coil and in so doing they induce a coun¬ 
ter-electromotive force which is in opposition to the 
impressed electromotive force. It can readily be 
seen that this counter-electromotive force tends to 
hold back the rise in current or make it lag behind 
the E. M. F. In the same way, when the current in 



FIGURE 169. 


the coil decreases in strength the lines of force clos¬ 
ing in on the wire add their E. M. F. to that of the 
impressed E. M. F. and tend to prolong the current, 
again causing the change in the current to follow or 
lag behind the E. M. F. This is shown by the 
curve (Figure 169), where C represents the cur¬ 
rent and V the E. M. F. This action is called self- 
induction. Self-induction in a circuit acts in the 
same way as resistance: it tends to cut down the cur- 



230 


WIRING DIAGRAMS 


rent. For an illustration: suppose the resistance of 
the wire in the coil just referred to was 5 ohms. A 
direct current of 110 volts would cause a current of 
110/5=22 amperes to flow through the coil. But if 
we were to send an alternating current at 110 volts 
through the coil we would find that the resulting cur¬ 
rent would be much less than 22 amperes and if we 
inserted an iron core in the coil the current would 
be still farther reduced, because the resistance of iron 
to the lines of force is much less than with air so 
that the lines of force would be increased in num¬ 
ber. The frequency of the current, or the rapidity 
of the alternations also effects the amount of current 
produced, the current being smaller the greater the 
number of alternations. 

A condenser connected in a circuit acts in a way 
similar to an inductance except that the condenser 
causes the current to lead the E. M. F. in phase. 
When an alternating current flows along a circuit 
across which a condenser is connected, as the E. M. F. 
in the line rises the condenser is gradually charged, 
the charge increasing in value as long as the current 
is rising. As the E. M. F. in the line begins to fall 
the E. M. F. across the condenser terminals lowers 
and the condenser begins to discharge into the line 
continuing to discharge until the impressed E. M. 
F. has passed through 0 and reached a maximum 
negative vah e. At this point the current again be¬ 
gins to flow into the condenser. It will be seen that 


TRANSFORMERS 


231 


while the E. M. F. in the line is passing from a 
maximum positive value to a maximum negative value 
that the condenser current is negative or flowing out 
of the condenser and while the E. M. F. in the line 
passes from a maximum negative value to a maxi¬ 
mum positive value the current in the condenser is 
positive. The condenser current reaches a maximum 
90 degrees in advance of the E. M. F. and for this 
reason is known as a leading current. 

In a circuit containing inductance or capacity, 
where the current is out of phase with the E. M. F. 
the current may be resolved into two currents, one of 
which is in phase with the E. M. F. and the other 90 
degrees out of phase with the E. M. F. This latter 
current is known as a wattless current and is greater, 
the greater the inductance or capacity in the circuit. 

If in a circuit containing inductance or capacity 
where the current is out of phase with the E. M. F., 
we would measure the power in watts, using a volt¬ 
meter and ammeter, W = C. E., we would get an 
apparent amount of power which would be greatly 
in excess of that actually consumed. The number of 
watts actually consumed could be measured by a 
wattmeter. The ratio of the number of watts actually 
consumed to the apparent watts is known as the power 
factor, or Power factor=Actual watts divided by 
apparent watts. As an example: suppose the volt¬ 
meter and ammeter showed 115 volts and 10 amperes 
which would be equal to 1150 watts and the watt- 



232 


WIRING DIAGRAMS 


meter shows 920 watts. Then 920/1150=80/100 
or .80 which is the power factor. The actual current 
doing work would amount to 8 amperes but as shown 
by the ammeter 10 amperes is flowing and the wire 
and fuses on such a circuit would have to be of suf¬ 
ficient size to carry 10 amperes. 


CHAPTER XVI. 


ARMATURES. 

Figure 170 is a diagram of a Gramme ring arma¬ 
ture. This style is often used with series arc light¬ 
ing machines. It is well suited for high voltages 
but not for heavy currents. 



FIGURE 170. FIGURE 171. 


The winding shown in Figure 171 is that of an or¬ 
dinary cylinder or drum armature. The wire wound 
on this armature as well as that of the preceding al¬ 
ways forms one continuous coil or loop. This can 
be seen by tracing the wire beginning at commutator 
bar 1 , thence to section a, around back of core to a' 
and then to commutator bar 2. From this bar to 6, 
then to b ' and commutator bar 3, etc. This is one 
of the simplest windings used, but many makers are 

233 



234 


WIRING DIAGRAMS 


using modifications of it; the principle of all, how¬ 
ever, being the same. 

Figure 172 shows a diagram of Thomson-Houston 
ring armature used for series arc lighting. This 
armature consists of three sections which terminate 
at three commutator segments from which current is 
taken off. The other terminals of all three sections 
terminate in a copper ring which joins all of them 
together. 



FIGURE 172. FIGURE 173. 


A diagram of the Brush armature, also for series 
arc lighting, is shown in Figure 173. The figure 
shows only two sets of coils, although in actual prac¬ 
tice many more are used. In this style of armature 
some of the coils are always on open circuit and it 
will be seen that there is no connection whatever be¬ 
tween the different coils except through the commuta¬ 
tor segments and the brushes resting upon them. 

Figure 174 illustrates the winding of an armature 
such as is used in single-phase alternating current 




ARMATURES 


235 


machines. The number of coils on the armature must 
always he equal to the number of poles in the fields. 
With dynamos of this kind quite often the fields are 
made to revolve and the current to the outside lines 
flows from the stationary coils on the frame. 



In Figure 175 a diagram of a three-phase, four- 
pole, star connected armature is shown. The wind¬ 
ing for each separate phase is similar to that of the 
single-phase armature. One end of each coil termi¬ 
nates in a collector ring; the other ends of all the 
coils meeting in one common connection. It will be 
noticed that there are three coils (one for each phase) 
for every pole piece, making twelve coils in alL 








CHAPTER XVIL 


SWITCHBOARDS-GROUND DETECTORS. 

Figure 176 shows the wiring and connections of 
the Western Electric Co.’s series arc switchboard. At 
the top of the board are mounted six ammeters, one 
being connected in the circuit of each machine. On 



the lower part of the board ‘are a number of holes, 
under which, on the back of the board, are mounted 
spring jacks to which the circuit and machine 
terminals are connected. For making connections be- 

- 236 












































































































SWITCHBOARDS 


237 


tween dynamos and circuits, flexible cables termi¬ 
nating at each end in a plug, are used; these are 
commonly called “jumpers.” The board shown has 
a capacity of six machines and nine circuits, and with 
the connections as showm machine 1 is furnishing cur¬ 
rent to circuit 1, machine 2 is furnishing current to 
circuits 2 and 3, and machine 4 is furnishing current 
to circuits 4, 5 and 7. In connecting together arc 
dynamos and circuits the positive of the machine (or 
that terminal from which the current is flowing) is 
connected to the positive of the circuit (the terminal 
into which the current is flowing). Likewise the neg¬ 
ative of the machine is connected to the negative of 
the circuit. Where more than one circuit is to be op¬ 
erated from one dynamo, the — of the first circuit is 
connected to the + of the second. At each side of 
the name plate (at 3, for instance) there are three 
holes. The large hole is used for the permanent con¬ 
nection, while the smaller holes are used for transfer¬ 
ring circuits, without shutting down the dynamo. 
Smaller cables and plugs are used for transferring. 
If it is desired to cut off circuit 5 from machine 4, a 
plug is inserted in one of the small holes at the right 
cf 4, the other plug being inserted in one of the holes 
at the left of 7. Circuit 5 would now be short cir¬ 
cuited, and the plug in the —[— of 5 can now be trans¬ 
ferred to the permanent connection in the -f- of 7, 
and the cords running to 5 removed. If it is desired 
to cut in a circuit, say circuit 6 onto machine 2, in- 


233 


WIRING DIAGRAMS 


sert a cord between the — of circuit 2 and the -f- of 
6 and another between the — of 6 and the -f- of 3. 
Now pull the plug on the cord connecting — of 2 
and the of 3 and insert the permanent connections. 
In cutting in circuits, if they contain a great number 
of lights, a long arc may be drawn when the plug be¬ 
tween 2 and 3 is pulled;* and it is sometimes advisable 
to shut down the machine when making a change of 
this kind. 



Figure 177 is a diagram of the Thomson-Hous- 
ton arc switchboard. The generators connect to hori¬ 
zontal brass strips fastened to the back of the board, 
as indicated by the heavy black lines. The circuits 
connect to similar strips fastened vertically to back 
of board but separated from the horizontal strips. 
These vertical strips extend below the horizontal 
strips and terminate in a number of plug holes shown 
at the bottom. Long plugs are provided suitably 
constructed to make connection betw r een any of the 
















































SWITCHBOARDS 


239 


horizontal generator strips and any of the vertical 
circuit strips. 1 he lines at the bottom indicate 
plugs connected by short cables and by tracing 
out the circuits it will be seen that all three are in 
series with generator 1. The positive sides of all 
dynamos are usually run to one side of the board and 
the positive sides of all circuits to the same side, so 
that only through gross carelessness could wrong 
plugging, as to polarity, exist. 

A, B, C, D and E, Figure 178, illustrate the suc¬ 
cessive steps necessary to change circuits 1 and 2 from 
dynamo 1 and 2 and connect them in series on dynamo 
2 . The solid black circles represent plugs. 

The first step is shown in B where the positive 
poles of both dynamos are placed in parallel by in¬ 
serting the two additional plugs. 

The second step is to withdraw the two first plugs 
shown in A. This places the two dynamos in series, 
D1 connecting direct to circuit 2 , as shown at C. 

The voltage of dynamo D1 may now be reduced 
and two plugs with cable connections inserted, as 
shown at D. This short-circuits dynamo D1 and 
leaves D2 carrying the load of both circuits. 

The plugs connecting D1 to the circuit may now 
be withdrawn, leaving the connections as at E, where 
dynamo D2 supplies both circuits. 

In F two circuits are shown as running in series 
on dynamo D1 and the insertion of plug H serves to 


240 


WIRING DIAGRAMS 


short-circuit and extinguish circuit 2. The plugs I, 
J and K may now be withdrawn. 



FIGURE 17&. 

In Figure 179 the switchboard connections and all 
necessary instruments for operating a single (shunt 
or compound) dynamo are shown. Such a board 
could be used on a small isolated plant. At the left 
a front view with the instruments is shown, while at 



















































































































































SWITCHBOARDS 


241 


the right is a rear view showing the connections. Re¬ 
ferring to the view at the left, V is a voltmeter and A 
an ammeter with scales suitable to the voltage and 
current used. PL is a pilot lamp. The ground de¬ 
tector switch GD is used to measure the insulation 
resistance to ground of each side of the system. In 



the position shown the voltmeter is connected directly 
across the bus bars. If the switch is moved to the 
right, the -|- bus bar is connected through the volt¬ 
meter to ground, and, by means of the reading ob¬ 
tained, using the formula given under the head of 
testing, the insulation resistance can be determined. 
Moved to the left, the insulation resistance of the 
other side of the system can be obtained. One of the 





























































242 


WIRING DIAGRAMS 


dynamo leads is carried to one terminal of the main 
switch M, while the other lead is carried through the 
circuit breaker CB to the other terminal of the switch. 
The circuit breaker is generally set to operate at a 
lower rise in current than the fuses on switch M, so 
that these fuses only blow in case the circuit breaker 
fails to operate. The circuit breaker is not absolutely 
necessary, but is generally installed in well designed 
plants. The small hand wheel R is connected to the 
rheostat mounted on the rear of the board. The 
switches 1, 2, 3 and 4 operate the feeder lines. On 
the rear of the board the three wires F, A -f- and 
A —, go to the dynamo, w T hile the line marked G is 
connected to some good ground, such as a w r ater pipe. 
The rheostat R is connected in series with the shunt 
field, and is used to regulate the voltage. AS is a 
shunt connected in series with one of the bus bars, 
the terminals of the shunt being connected to the am¬ 
meter. This shunt is generally furnished with the 
ammeter. In case an ammeter which carries the en¬ 
tire current is used, leads must be carried to the am¬ 
meter so that it will be connected in series with one of 
the mains. The feeder lines are connected to the up¬ 
per terminals of switches 1, 2, 3, and 4. The ground 
detector, pilot lamps and voltmeter are connected to 
the bus bars through the cutout CO, standard No. 
14 rubber covered wire being used on these circuits. 


GROUND DETECTORS 


243 


GROUND DETECTORS. 

t 

In Figure 180 a ground detector switcl suitable 
for mounting on a switchboard is shown. Two arms 
A, A', pivoted at their upper ends, are connected to¬ 
gether with an insulating bar B. These arms make 
contact at their lower ends with two brass strips and 
a contact button which are connected to the bus bars 
and ground respectively. When the arms are moved 
to the left the -f- bus bar is connected to ground 



FIGURE 180. 



FIGURE 181. 


through the voltmeter V. By means of the reading 
obtained the insulation resistance to ground of the 
— side of the line can be calculated by using the 
formula given further on. By moving the arm to the 
right the insulation resistance of the + side of the 
line can be obtained. 

Figure 181 shows a lamp ground detector. On a 
IV 0-volt system two ordinary 110-volt lamps are con¬ 
nected in series, while the line connecting the lamps 

















244 


WIRING DIAGRAMS 


is connected to ground through a snap switch S. 
When current is on, the two lamps will bum with 
equal brilliancy at a low candle-power. When the 
switch S is closed, if the two lines are clear the bril¬ 
liancy of the lamps will not be affected; but if there 
is a ground on the -f- side of the line lamp 2 will 
burn brighter, the brightness depending on the re¬ 
sistance of the ground. If there is a dead ground 
the lamp will burn at full candle-power, lamp 1 not 
burning at all. If the ground is on the — side of 
the line lamp 1 will burn brighter. 



Figure 182 shows another method of using a volt¬ 
meter as a ground detector. The arms A A' are 
hinged at the upper ends and swing separately. Anri 
A moved to post 1 gives.the reading on the + side, 
and arm A' moved to post 1 gives the reading on the 
— side of the line. 

Figure 183 shows another method, using two sin¬ 
gle-pole double-throw knife switches. Throwing 















GROUND DETECTORS 


245 


switch 1 to low r er position connects the ■— bus bar to 
ground, and gives the insulation resistance of the -f- 
side of the line. 

Another form in which two double-point push but¬ 
tons are used is shown in Figure 184. In normal 
position contact is made to the upper points so that 
the voltmeter is always connected across the bus bars. 
Pushing button 1, the insulation resistance of the + 
side of the line can be obtained, and pushing button 
2 the — side. 



FIGURE 184. FIGURE 185. FIGURE 186. 


Three-way snap switches are used for the same 
purpose in Figure 185. 

When several machines are in operation the method 
shown in Figure 186 can be used. With this arrange¬ 
ment the voltage can be taken on any one of several 
lines or machines, and also the insulation resistance 
to ground. The voltmeter connection is made by 
means of flexible cords terminating in plugs, which 
fit in the jacks, which in turn are connected to the 
machine leads or to the various circuits. 



























246 


WIRING DIAGRAMS 


The switch shown in Figure 187 is designed for 
use where two dynamos are run in parallel. An arm 
A pivoted at the center is equipped with brass strips, 
which, by moving arm A, make contact between the 
center curved piece and the contact points 1, 2, 3 and 
4. With the arm moved down the voltmeter is con¬ 
nected to machine No. 1, and with the arm moved up 
the voltmeter is connected to machine No. 2 . By 
a slight movement of the arm the voltage of either 




FIGURE 188. 


C 


FIGURE 189. 



machine can be taken. This is useful where a dynamo 
is being brought up to speed to connect on to the bus 
bars. 

Figure 188 shows a lamp ground detector for use 
on a three-wire system where the neutral is not 
grounded. In nearly all three-wire systems the neu¬ 
tral is either permanently grounded or becomes 
grounded so that ground detectors are not used, a 
ground on either of the outsides blowing a fuse. 

Figure 189 shows a method of locating grounds on 
























GROUND DETECTORS 


247 


a series arc line, where lamps are burning. A num¬ 
ber of incandescent lamps are connected in series, the 
last lamp being connected to ground. Two wires are 
carried to the double-throw switch S, one wire being 
connected to each side of the circuit. From the mid¬ 
dle of the double-throw switch a flexible connection 
is carried to the first lamp, and the brightness of the 
lamps noted. If the lamps do not burn up to full 
candle power, connection is made at some lamp nearer 
the ground, and this continued until the lamps burn 
at full brightness. When this point has been reached 
the number of lamps is counted, and if 100-volt in¬ 
candescent lamps are used it will be seen that there 
are just twice as many arc lamps burning between 
that side of the machine and the ground as there are 
incandescents burning, for an arc lamp takes approx¬ 
imately 50 volts. In the diagram suppose there is a 
ground on the arc circuit at X; then, with the con¬ 
nection to the incandescent lamps as shown in the 
dotted lines, the lamps will burn at full brightness. 
Care should be taken in handling apparatus of this 
kind on account of the high voltages on arc circuits 
on which there are a number of lamps. 

Figure 189a shows diagram of ground detector con¬ 
nections on a two phase circuit. A lamp is connected 
in parallel with the inductance and by connecting the 
lamp to different points as 1 or 4 for instance, an idea 
of the resistance to ground can be formed. If the 
lamp will burn brightly at point 4 it indicates that the 


248 


WIRING DIAGRAMS 


insulation resistance of the line to ground is much 
lower than it would be if it would have to be con¬ 
nected at point 1 to burn brightly. 



A similar plan for three phase circuits is followed 
in Figure 189b. 

As with other ground detectors, if the ground switch 
is connected to the leg that is grounded the lamp will 
not burn at all. 



























GROUND DETECTORS 


249 


Figure 189c shows ground detector arranged for 
high potential service. Two voltmeters are connected 
through two transformers as shown. If the line is 
clear the two voltmeters show low readings which are 
equal for both instruments. With a ground coming 
on at A and the switch closed to guard the meter at the 



FIGURE 189c. 


left will indicate lower and that on the right higher* 
With a ground coming on at C the indications will be the 
reverse, while with a ground at B both voltmeters 
will read higher. 



















CHAPTER XVIII. 


STORAGE BATTERY CONNECTIONS.. 

Figure 190 shows a diagram of connections of a 
storage battery and booster suitable for an ordinary 
electric light installation, where it is desired to use 
the battery at time of heavy load to assist the genera¬ 
tor, and to use the battery alone at time of light load. 
The booster B, which is driven by the motor M, the 
two forming a motor generator set, is connected in 
series with the battery circuit, and serves to raise the 
voltage to that necessary to charge the batteries. R 
is a rheostat in the field of the booster by which the 
E. M. F. can be regulated. 

To charge, the double-throw switch S is thrown 
downward and the single-pole switch is closed, the 
end-cell switch E being placed on point 5 so that ai* 
the cells are in circuit. The motor is now started, 
and when it is up to speed the arm of the motor rheo¬ 
stat closes the charging circuit at C. To discharge, 
throw the end-cell switch E to point 1 and throw 
double-throw switch S upward. The battery is then 
in parallel with the generator. To run with the bat¬ 
teries alone open switch MS. 

As the E. M. F. of the battery falls, more end- 
cells are switched in by moving switch E to points 

250 


STORAGE BATTERY CONNECTIONS 251 



(I + 


figure 190 



























































































































252 


WIRING DIAGRAMS 


2, 3, 4 or 5. A separate voltmeter is generally in¬ 
stalled so that the readings of the voltage may be 
taken from the end-cells separately, to prevent over¬ 
charging or exhausting them. 

In power work, where variations in voltage are 
greater and not of so much importance, storage bat¬ 
teries are often connected directly across the mains 




hi 


mi 


I 



a 

1 

0 

* 


, 

mWimWWI 

• 




Q 





\y 

i 



J) 


FIGURE 190a. 


without a booster. In such cases the battery will take 
current from the mains when the load is light and 
the voltage correspondingly high, and give current 
into the line when the voltage becomes low due to 
heavy loads. 

Figure 190a shows connections of a storage battery 
to be charged without the use of a booster. For 
charging, the battery is connected with the two halves 




































































STORAGE BATTERY CONNECTIONS 253 



FIGURE 190b, 



































































































































































































































254 


WIRING DIAGRAMS 


in parallel. As shown the battery is ready for charge 
if the single pole switches at the center are closed 
downward, and those at the right and left placed to 
their proper positions with the end cells in circuit. 
As the E. M. F. of the battery builds up sections of 
the resistance R, beginning at the right, are cut out. 
An ammeter is provided in each leg so that the rate of 
charge of each half of the battery may be observed. 
When fully charged the main switch is opened, switch 
S is then also opened, S' is closed and the single pole 
switches at the center of the battery are closed on the 
upper points. This places the two halves in series 
and fit for connection to the line. The end cells should 
be adjusted so that the voltage of the battery is about 
equal to that of the line before it is thrown in. 

Figure 190b shows diagram of storage battery as 
arranged by the Gould Co., to be charged from a high 
voltage (150 volt) dynamo. A separate set of end cell 
switches is provided for charge and discharge so that 
both may be taking place at the same time. There 
are two circuit breakers, the one at the right is pro¬ 
vided with a reverse current trip to protect the dynamo 
in case its voltage should fall so that the battery could 
send current through it. 

In Figure 190c a large automobile charging station 
is shown. As a battery is connected for charge the 
corresponding switch S is thrown upward. This 
allows current to pass through the ammeter A, and 
the rheostat is now set so that the current flow is at 


STORAGE BATTERY CONNECTIONS 255 


the proper rate. When this is done the switch is 
thrown downward, this leaves the ammeter free for 
use with the next charge. By entirely opening the 
switch and inserting plug at P in the corresponding 
circuit the voltage of any battery can be taken. 



An end cell switch as sometimes used is shown in 
Figure 190d. This switch avoids short circuiting the 
cells while changing from one to the other, and also 
avoids opening the circuit entirely. The arm A makes 
the permanent connection, but while it is moving 
from one segment to the other the other arm carries 
the current through R. 





























































256 


WIRING DIAGRAMS 


The Cooper Hewitt Mercury Rectifier, adapted to 
rectifying alternating currents for the purpose of 
charging storage batteries, is shown diagrammatically 
in Figure 190e. B is a glass bulb which carries two 
electrodes at its upper extremity and a quantity of 
mercury in the bottom. The globe is further filled 
with mercury vapor which posseses the peculiarity 



that it allows current flow from the upper electrodes 
P into the lower, but does not allow a reversal of this 
current. 

In the bottom of the bulb there are also two elec¬ 
trodes, one in the mercury and the other a little above 
it. In order to start the operation it is necessary to 
tilt the bulb sufficiently so that the mercury bridges 
the two lower electrodes. This starts current flow 
through the auxiliary wires R. When the bulb is 
allowed to return, this circuit is interrupted and the 
current from whichever of the two upper electrodes 


















STORAGE BATTERY CONNECTIONS 257 


happens to be positive at the time continues in its 
place. Should the current ever cease entirely, even 
for an instant, the bulb would require to be tilted 
again. In order to avoid this occurrence the reactance 
E is provided; this produces a phase difference be¬ 
tween the impulses in the supply circuit and those 



passing into the battery so that the currents overlap, 
and the current from one electrode does not cease until 
that from the other has been started. The alternating 
current supply is connected at A C. 

Figure 190f shows a small storage battery con¬ 
nected to be charged from a series arc circuit. While 






























258 


WIRING DIAGRAMS 


the switcn 1 remains in the position shown no current 
passes through the battery. If the switch is pulled 
downward part of the current passes through the resist¬ 
ance R and part of it through the battery. The dif- 



\/L 

“\ 


/\ 


ference of potential existing at the terminals of R will 
be equal to the product of the resistance of R and the 
current flowing. This must always be a little greater 
than the E. M. F. of the battery or the battery will 
discharge through the resistance. 















CHAPTER XIX. 


TESTING. 

Figure 191 is designed to illustrate a method of 
testing out rough wiring when lights or fixtures are 
to be connected. All wiring may be considered com 
cealed except the ends at outlets, and it is assumed 
that nothing is known of how the wiring is run in. 



The first step is to separate all wires at outlets, so 
there may be no wrong connections. Next connect 
an ordinary bell and battery as shown in the figure 
and fuse up the circuit. If the bell now rings, there 
must be a short-circuit in the wiring leading direct 
from the cutout, since we have disconnected all other 
wires. To locate this it will be necessary to get ac¬ 
cess to the wiring, and it may be necessary to tear 
off plaster or break into walls. Oftentimes it is bet¬ 
ter to abandon a circuit with such trouble as this and 

259 


































260 


WIRING DIAGRAMS 


run in a new one. If the circuit is found clear, the 
next step is to temporarily bring together the bare 
ends of all the wires found at any of the outlets until 
a ring from the bell is obtained. When a ring is ob¬ 
tained it will indicate that the circuit feeds direct to 
this outlet from the cutout. Next pick out at this 
outlet the two wires which together produce a ring. 
These two wires come direct from the cutout, and 
may now be marked as such. 

In the figure it is intended that the light 1 shall 
be controlled by the switch S', and the light 2 by the 
switch S"; the lights 3 and 4 are not provided with 
switches, but the large chandelier C is to be con¬ 
trolled by the double-pole switch DS. 

The next step will be to find the two wires leading 
to switch S'. To accomplish this, close the switch 
and bring any two of the wires found at outlet 1 in 
contact with those coming from the cutout; when 
the proper wires have been thus connected the bell 
will ring. One of the switch wires may now be con¬ 
nected permanently to one of the circuit wires coming 
from the cutout, while the other is to be connected 
to one side of the lamp or fixture. The other wire 
coming from the cutout goes to the other side of the 
lamp or fixture. Lamp 1 is now completely connected 
and under control of switch S'. The quickest way to 
find the proper connections for lamp 2 and switch S" 
is by bunching all the wires at 2, and then trying at 
1, any two wires to those coming from the cutout 


TESTING 


261 


until the bell rings. The two wires which cause this 
ringing lead direct to lamp 2, and may now be con¬ 
nected to the wires leading from the cutout, care be¬ 
ing taken that they are connected so as not to come 
under control of switch S'. Next, separate the wires 
at 2, and find those which when brought together 
cause the bell to ring; one of these must be connected 
direct to the lamp or fixture, while the other is con¬ 
nected to one of the remaining wires. This leaves 
one wire, and it connects to the other side of the lamp 
and completes the connection of lamp 2 and switch 
S". The four remaining wires at 1 may be found 
in a similar manner, care being taken that they are 
also connected behind the connections of switch S'. 
Two of the six wires at outlet C may now be con¬ 
nected direct to those coming from outlet 1. After 
this, go to switch DS and find the wires coming from 
outlet 1 and the cutout (by ringing the bell), and 
connect them to the proper points on the switch. The 
remaining wires connect to the other pole of the 
switch and to the chandelier. The wires leading to 
lamp 3 may be doubled up under the screws of the 

cutout terminals. 

For testing of this kind the bell shown is the most 
convenient instrument, since it is audible at quite a 
distance, and a circuit as described often extends 
through several rooms. A magneto may also be used, 
with an assistant to turn the crank, or if the circuit 
at the cutout is short-circuited the wireman may 


262 


WIRING DIAGRAMS 


carry it with him, making connections wherever he 
wishes to test. If the cutout center is “alive” a lamp 
may be placed instead of one of the fuses, and the 
wireman may carry another with him for testing. A 
galvanometer or telephone receiver may also be used 
in this way, the battery alone being connected at the 
cutout center. 

Figure 192 shows the main and branch wiring of 
a two-wire incandescent system, all complete and 
ready for final test and connection. In the first place 
it is necessary to close all the switches and insert all 
fuses, and a test for short circuits or faulty insula¬ 
tion between opposite poles may then be made by 
placing a lamp L in circuit in place of one of the 
main fuses. If current is now thrown on the lamp 
will light in case there is any serious defect in the 
insulation between opposite polarities in any part of 
the system. In case there are any two or three-way 
switches controlling lights from several places, it 
will be necessary to turn one of these on each circuit 
after the first test has been made and then make an¬ 
other test—since one cannot well be certain whether 
such switches close a circuit or not unless a lamp can 
be seen to bum. It will also be advisable to do this 
with single and double pole switches, and may often 
be easier than removing covers from snap switches to 
see whether they are on or off. Snap switches will 
often indicate by the sound of the snap whether they 
are on or off, but this is not always reliable. 


TESTING 


263 


If a more thorough test than that given by the 
lamp is required, it may be made with any one of the 
four instruments shown. The voltmeter may be con¬ 
nected in place of the lamp. If the system is perfect 
the voltmeter will indicate nothing, while it a short- 



circuit exists it will indicate the full pressure. A tele¬ 
phone receiver may also be used in the same way, if 
properly w T ound, and if the system contains no lead- 
covered wires or iron pipe and is not too laige. If 
the Wheatstone bridge W, or magneto M is to be 

































































264 


WIRING DIAGRAMS 


used for this test, both main fuses must be removed 
and connection made to both wires as shown with these 
instruments. Lead-covered wire, or wire in iron pipe, 
will also interfere with testing by a magneto, a ring 
sometimes being obtained when the insulation of the 
system is perfect. 

The figure also shows the voltmeter V and the 
telephone receiver fitted up with battery to test the 
insulation resistance to earth of lines having no cur¬ 
rent; the same connections may be made with the 
magneto or Wheatstone bridge, and both main wires 
may be connected at once as shown 
More detailed explanation and formulas for testing 
with the voltmeter and Wheatstone bridge will be 
given further on. 

When it is desired to ascertain the current passing 
along the mains, an ammeter may be connected in 
place of voltmeter V as shown. To test the in¬ 
sulation resistance accurately, the system should not 
be alive, although approximate tests may be made 
with a voltmeter or ground detector lamps connected 
as shown in Figure 192. This method of testing live 
circuits is practical only on small systems, since the 
system cannot be subdivided, and the indications are 
accurate only so long as defects are confined to one 
side of the line. With large three-wire systems it is 
quite usual to have the neutral wire grounded, and 
these methods could not be used at all. 

In Figure 192 there are shown two ground de- 


by dotted lines. 


TESTING 


265 


tector lamps C and D, and by means of a key or 
switch the wire between them may be connected to 
ground. As long as this key is not brought in con¬ 
tact with the ground wire, both lamps burn dimly in 
series and with equal brilliancy, and if no ground 
exists in any part of the system, depressing the key 
will not affect the lamps. Should, however, a ground 
exist, say at G, closing the key will establish a path 
through the ground and through lamp C to the op¬ 
posite side of the circuit. If the ground is of very 
low resistance the lamp C will burn at full candle 
power, while D will not burn at all. Should the 
ground be of high resistance there will be but little 
difference in the brilliancy of the lamps. 

The connections of the voltmeter are based on the 
same principle. The switch S moved one way makes 
connection with the positive pole through the volt¬ 
meter to the ground, and moved the other way makes 
connection with the negative pole through voltmeter 
to ground. In the position shown the switch is clear 
of the ground, and connects the voltmeter to the 
lighting mains so as to obtain full pressure. The 
formula for use with the voltmeter when the exact 
value of the resistance is to be determined is X = R 

—— | where E is the full voltage of the battery or 

other source of current as indicated on the voltmeter, 
E' is the reduced reading obtained through the volt¬ 
meter and the resistance to be measured, and R the 




WIRING DIAGRAMS 


266 

resistance of the voltmeter, X being the value of the 
unknown resistance. This formula is based on the 
supposition that the voltmeter and the resistance to 
be measured are in series, and that all current pass¬ 
ing through the resistance being measured also passes 
through the voltmeter. 

Referring to Figure 192, so long as G is the only 
defect on the system allowing current to flow, the 
above formula will give us the correct resistance; as 
soon, however, as G' is introduced the formula be¬ 
comes unreliable, since G' is a shunt around the volt¬ 
meter and robs it of current. The current passing 
through the voltmeter no longer depends only on the 
roltmeter resistance and that of G, and therefore the 
. eadings can no longer be used as a basis of calcula¬ 
tions. As a matter of fact, if the voltmeter test on 
a live system as shown in the figure indicates a low 
gv'ound on one side, as, for instance, G', it will usual¬ 
ly show the other side very high. The ground de¬ 
tector lamps are subject to the same limitations, but 
although they and the voltmeter cannot be relied upon 
for accurate testing, both are very useful when ar¬ 
ranged so that tests can be made several times per 
day, so as to give means of detecting a ground as 
soon as it comes on. 

In Figure 193 is given a diagram of the Wheat¬ 
stone bridge. This instrument is generally used 
where accurate measurements of resistance are to be 
made, and on account of its wide range it is the most 


TESTING 


267 


Useful instrument for this purpose. It will be seen 
that current from the battery entering at 1 has two 
paths open to it, one through B and X and the other 
through A and R, to the other pole of the battery. 
If the resistances A and B are equal, then an equal 
quantity of current will pass through each to the 
points 2 and 3 respectively. If the resistances R and 
X are also equal (though they may be much greater 


1 



FIGURE 193. 


or smaller than A and B) they will also carry away 
equal quantities of current. Under these conditions 
no current will pass through the galvanometer G. 

If the resistance of A is made ten times as great 
as that of B, then A will carry only one-tenth as 
much current to 2 as B will carry to 3; and if R is 
made ten times as high as X, then R will carry away 
all the current from 2, while X takes away all current 
from 3, and still no current will flow through the 
galvanometer. So long as A is to R as B is to X, 
no current will pass through the galvanometer. When- 







268 


WIRING DIAGRAMS 


ever this relation is disturbed, some current will pass 
through the galvanometer, either from 2 to 3 or 3 to 
2. If X is entirely open, all the current flowing 
through B to 3 will pass through the galvanometer 
to 2 ; and, again, if R is ,of higher resistance than X, 
while A and B are equal, some current will pass from 
2 through the galvanometer to 3. 

To make the resistance of A, B and R variable, 
brass plugs are provided which may be inserted in 
the openings shown so as to form a shunt to the re¬ 
sistance bridged around the opening. In each of 
the proportional arms A and B two openings are al¬ 
ways plugged, and the one unplugged is the resist¬ 
ance through which the current must pass. In R all 
plugs are removed to get the total resistance, while to 
get the lowest resistance all openings but the lowest 
are plugged. 

To measure any resistance proceed as follows: If 
the unknown resistance connected at X is not greater 
than the total of R, or smaller than any one plug in 
R, A and B may be plugged equal; for instance, 
plugs inserted in the openings 1000 and 100 on each 
arm, leaves on each side ten ohms in circuit and 
leaves the greatest battery strength for the galvano¬ 
meter. Now plug R so the resistance will be quite low 
and press the key; if this gives any deflection note 
whether it is to the right or left. If a decided de¬ 
flection has been obtained, remove a number of plugs 
until the resistance of R is quite high and again press 


TESTING 


269 


4ie key. If the deflection now obtained is in the op' 
posite direction of the former, the value of the resist¬ 
ance is something between the first value of R, and 
the second, and repeated trials are necessary until no 
deflection is obtained. No deflection may also be 
caused by a weak battery. If everything is in order, 
increasing or lessening R should cause reverse deflec¬ 
tions. 

When balance is obtained with A and B equal, the 
sum of the unplugged resistances in R will give the 
value of X. If X is greater than R, we cannot ob¬ 
tain balance unless B is greater than A; and, con¬ 
versely, if X is less than the smallest resistance in R, 
balance cannot be obtained unless B is smaller than A. 
Whenever balance is obtained, A is to R as B is to X. 
The values of A, B and R are known, and, since it is 
a well-known rule of arithmetic that in any propor¬ 
tion the product of the means equals the product of 
the extremes, we can find the value of X, since 


axx=bxr, 


BxR 

A 


=X, or in other words to 


find the value of X we must multiply the sum of the 
unplugged resistances in R by B and divide by A. 

If, in Figure 193, A is unplugged to equal 10 and 
B to 1000, when balance is obtained X will equal 100 
times R. If B is unplugged to equal 10 and A at 
1000, X will equal 1-100 part of R. The total range 
of the resistance that can be measured by the arrange- 



270 


WIRING DIAGRAMS 


ment shown in this figure is from 1 ohm to 600,000 
ohms. 

Figure 194 shows one commercial form of the 

Wheatstone bridge. In this form movable arms are 

% 

used to adjust the resistance instead of plugs. The 



resistance to be measured is connected to the binding 
posts marked X, and when balance is obtained the 
sum of the resistances indicated by the lower arms is 
divided by D and multiplied by M. The key is ar- 

































TESTING 


271 


ranged to close the battery circuit before closing the 
circuit through the galvanometer. This is important, 
especially where inductive resistances such as the coils 
of electro-magnets are to be measured, and prevents 
inductance and discharge of these magnets from dis¬ 
turbing the galvanometer reading. 



Figure 195 shows another form of Wheatstone 
bridge, and Figure 196 a diagram of the connections. 
With this form the resistance to be measured is con¬ 
nected at X, and if it is greater than R the two plugs 
in the center are arranged as shown in black. When 
balance is obtained X equals the sum of the un ¬ 
plugged resistances in R multiplied by B and divided 
by A. With the plugs arranged in the opposite holes 
between A X and B R, X equals the unplugged re¬ 
sistances of R multiplied by A and divided by B. 









































272 


WIRING DIAGRAMS 


As will be seen from Figure 193 the multiplying 
proportional coil is the one in series with the un¬ 
known. In this form of bridge it is possible to place 
either one of the coils in series with the unknown and 
hence we may use either one to multiply and the other 
to divide. This greatly increases the range of the 
instrument with the same amount of resistance. 



With a plug inserted between R and X, the other 
two plugs being left out, the box may be used as a 
straight resistance box. The galvanometer key has p. 
back contact which closes the galvanometer circuit on 
itself when released, and tends to stop the needle from 
swinging. 

Oftentimes these boxes are not equipped with bat¬ 
tery, and instead have two binding posts to which 
battery may be connected. If the battery in either of 
the above were connected at X the galvanometer nee¬ 
dle could be made to deflect in one direction only. 


















CHAPTER XX. 


LIGHT. 

The intensity of the light varies as the square of 
the distance from the source. This is rigidly true 
only at such distances where the source of light may 
be considered as a mathematical point having no 
physical dimensions. Thus the intensity of an elec¬ 
tric light is not four times as great at a distance of 
two inches as at four inches. 

A 16 candle-power lamp is usually allowed for ev¬ 
ery 100 square feet in ordinary rooms, when not sus¬ 
pended more than seven feet from the floor. With 
dark colored walls, or where a very bright light is de¬ 
sired, more lamps should be provided. 

The efficiency of lamps varies greatly with differ¬ 
ent candle-powers, a fair approximation being given 
below: 

32 candle-power lamp requires from 100 to 110 watts 


u 

66 

66 

66 

66 

50 

66 

56 

66 

66 

66 

66 

“ • 

66 

30 

66 

33 

66 

66 

66 

66 

66 

(( 

19 

66 

21 

66 


After lamps have been used for some time the ef¬ 
ficiency is reduced somewhat and the current con¬ 
sumption increased. 


273 


274 


WIRING DIAGRAMS 


The candle-power of any incandescent lamp in¬ 
creases much more rapidly than the current supplied 
to it, so that the higher efficiency demands full volt¬ 
age for the lamp. If long life is desired they should 
be operated at low voltage. Below is given a table, 
taken from the General Electric Company bulletin, 
showing the variation in candle-power and efficiency 
of standard 3.1 watt lamps due to variations in volt' 
age: 


Percent of normal 
Voltage. 


90 

91 

92 

93 

94 

95 

96 

97 

98 

99 
100 
101 
102 

103 

104 

105 

106 


Percent of Normal 
Candle-Power. 


53 
57 
61 
65 
69 # 
74 
79 
84 
89 
94 * 
100 
106 
112 
118 
124* 
131 * 
138* 


Efficiency in Watts 
per Candle 


4.68 

4.46 

4.26 

4.1 
3.92 
3.76 

3.6 
3.45 
3.34 
3.22 

3.1 
2.99 
2.9 
2.8 

2.7 
2.62 
2.54 


Example: Lamps of 16 candle-power, 105 volts, 
and 3.1 watts, if burned at 98 per cent, of normal 
voltage, or 103 volts, will give 89 per cent, of 16 
candle-power, or 14^4 candle-power, and the efficiency 
will be 3.34 watts per candle-power. 











LIGHT 


275 


In Figure 197 the various curves show the relation 
between the candle-power and voltage, current and 
watts in an incandescent lamp, the curves having been 
plotted from a 100-volt, 16 c. p. lamp. Taking the 
curve marked Volts and C. P. it will be seen that at 
70 volts the c. p. was at 2, while at 100 volts the c. p. 
was at 15. As the voltage rises the candle-power in¬ 
creases very rapidly, reaching 25 c. p. at 110 votts 
and 55 c. p. at about 127 volts. 



The upper or positive carbon of an arc lamp burns 
away twice as fast as the negative with continuous 
currents, but only about 8 per cent, faster with alter¬ 
nating currents. 

To get full benefit out of the carbons they should 
be protected from gusts of wind, as these often blow 
out the arc and cause rapid consumption of the car¬ 
bons. 


































276 


WIRING DIAGRAMS 


A very simple method of comparing the candle- 
powers of different lamps is that known as Bunsen’s. 
Set up the lamps to be compared, and, taking a piece 
of paper with a grease spot on it, adjust it between 
the two lamps until the spot becomes invisible. The 
candle-powers of the two lamps are then in the same 
proportion as the squares of the distances from the 
paper. 

The absorption of light by globes is given as fol¬ 
lows: 

Clear Glass, 10 per cent. Holophane, 12 p«r cent. 
Opaline, 20 to 40 per cent. Ground, 25 to 30 per 
cent. Opal, 25 to 60 per cent. 

An arc light gives out from one-twentieth to one- 
fortieth as much heat as gas light of equal candle- 
power. 

An incandescent light gives out from one-fifth to 
one-tenth as much heat as a gas jet of equal candle- 
power. 

One 5-foot gas burner (16 c. p.) vitiates as much 
air as four men. 


CHAPTER XXI. 


WIRING TABLES. 

The wiring table No. 1 is arranged in the follow¬ 
ing manner: For each size of wire and each voltage 
considered there is given (under the proper voltage 
and opposite the number of the wire under the head¬ 
ing B. & S.) the distance it will carry 1 ampere at a 
loss of 1$. The same wire will carry 2 amperes only 
half as far at the same percentage of loss and again 
will carry 1 ampere twice as far at double the per 
centage of loss. 

From these facts we deduce the rule of this table 
which is: Multiply the distance in feet (one leg only) 
by the number of amperes to be carried and divide the 
result by the percentage of loss to be allowed. Take 
the number so obtained and under the proper voltage 
find the number nearest equal to it. Opposite this 
number under the heading B. & S. will be found the 
size of wire required. To illustrate: We have 22 
amperes to carry a distance of 135 feet and the loss 
to be allowed is 3 per cent, at 110 volts. 

22X135=^=99° 

We take the number 990, turn to column for 110 volts, 
and find 841, which is not sufficient. The next above it 

277 



278 


WIRING DIAGRAMS 


is 1060, which corresponds to No. 7 wire. With this 
wire our loss will be slightly less than 3$, w'hile with 
No. 8 it would be somewhat in excess of 3$. 




For three-wire systems using 110 volts on each side, 
the column marked 220 volts should be used. The 











WIRING TABLES 


27& 


column marked 440 volts is provided for three-wire 
systems using 220 volts on each side. The sizes de¬ 
termined will be correct for all three wires in both 

cases. 

The columns at the right, marked motors, are ar¬ 
ranged in the same way, the only difference being 
that, for greater convenience, they are figured m H. 
P. feet instead of ampere feet. For this reason we 
multiply the distance in feet by the number of horse¬ 
power to be transmitted and divide by the percentage 
of loss, all other operations remaining the same as 

under lights. _ 

When any considerable current is to be carried 

only a short distance the wire indicated by the desired 
loss will very likely not have sufficient carrying capac¬ 
ity ; it is, therefore, always necessary to consult the 
table of carrying capacities. 


Light and Motor Wiring Table. 


280 


WIRING DIAGRAMS 


o 


i 


Resis. 

per 

foot 

.002628 

.002084 

.001653 

.001311 

1 .001040 

.000824 

.000654 

.000519 

.000411 

.000326 

.000259 

.000205 

.000163 

.000129 

.000102 

.000081 

.000064 

.000051 

.0000431 

.000036 

.0000308 

.000027 

.000024. 

.0000215 

.0000108 

.0000054 

H 

H 

£ 

O 

Ah 

H . 

Cfi 

« H 

O J 

500 

Oi'TOOiO 
I s * C4 rH lO ^ 

lO £>> 05 rH 

rH rH 

1821 

2318 

2918 

3684 

4636 

5858 

7389 

9294 

11757 

14762 

18733 

23701 

29745 

35107 

42145 

49017 

56179 

63217 

70235 

140470 

280961 

440 

$8388 

lO£> OOrH 

1408 

1792 

2256 

2848 

3584 

4528 

5712 

7184 

9088 

11488 

14480 

18320 

22992 

27136 

32576 

37888 

43424 

48864 

54288 

108576 

217168 

>5 

to 

M 

O 

H 

O 

220 

(N0«0^0 

HTft^C^OO 

(NOOH(MCO 
uo CO H 05 

co ^ io i> oo 

1132 

1428 

1796 

2272 

2872 

3620 

4580 

5748 

6784 

8144 

9472 

10856 

12216 

13572 

27144 

54292 

3 

Oil 

CCiO^^OO 
CO lO 

00 rH 00 ^ 
00 rH H* l> <N 
H rH H 04 

CO 05 00 00 
OQiOrf CDH 
C4 CO ^ UO l> 

to lO I> CD co 

O ^ CO 05 CO 

a h h co o 

rH H H Cl 

2368 

2714 

3054 

3393 

6786 

13573 

Car. 

Cap. 

•«*« 

rH • rH • (N 

• CO • co ^ 

• CO • ^ iO 

65 

76 

90 

107 

127 

o o io o 

lOD-nCON 
H H d Cl Cl 

OOOOOO 
o CO CO 05 lO to 

CO CO CO CO co o 

rH 

cc 

<8 

m 

Gauge. 

HCOC^HO 

HHHHH 

o> 00 t'- CO lO 

CO Cl H O 

00 

000 

0000 

250000 

300000 

350000 

400000 

450000 

500000 

1000000 

2000000 


440 

<DiM(N QO 

CO iO CO 00 rH 

00 O CO CO H 

H H H (N 

OtOClOO 
COOHiOH 
CO CO <M CO I> 
C4 CO iO CO 

CO CO ^ 00 

C5 CO 05 LO CO 

H N H O lC 
00 O CO H 

H H H Cl 

O co CD O 00 
CO CO co o 

rH CO rH r-H rH 
H COrH H 

<N CO ^ iO CO 

71428 

81480 

91664 

102324 

203700 

407404 

H 

W 

E 

9 

CO 

220 

00 CO CO O 00 

HiOOGCO 

rH 

1330 

1682 

2120 

2676 

3374 

4248 

5366 

6748 

8527 

10784 

1 

O CO 00 O H 
CO 00 CO CC LO 
iO r-UC iO lC 
CO 1> H LC O 
H H Cl Cl CO 

35714 

40740 

45832 

51162 

101850 

203702 

55 H 

►H 

O 

w 

© 

►A 

Oil 

C5 co co o o> 

O CO CO 
(M (M CO ^ UO 

665 

841 

1060 

1338 

1687 

h* CO r*< (N 
<M 00 l> CO 05 

H co CO Cl CO 

Ol (M CO ^ iO 

6790 

8594 

10784 

12790 

15277 

17857 

20370 

22916 

25581 

50925 

101851 


52 

98 

124 

158 

200 

250 

^ rH ^ 00 

HOOCOO 
CO CO lO CO 

1000 

1271 

1595 

2011 

2543 

3228 

4053 

5090 

6032 

7222 

8441 

9629 

10833 

12093 

24074 

48148 


i 




































WIRING TABLES 


281 


For lights, find the ampere feet (one leg) and di¬ 
vide by the per cent, of loss. Under the proper volt¬ 
age find the number equal to this or the next larger; 
opposite this number in the column marked B. & S., 
will be found the size of wire required. 

For Motors, proceed in the same way, using H. P. 
feet instead of ampere feet. 

It may often be desired to find the loss in an es¬ 
tablished circuit carrying a certain load. This may 
readily be determined from this table by observing 
the following rule: Find the number of ampere feet 
and, selecting the column headed by the proper volt¬ 
age, divide by the number opposite the size of wire 
used. For example, we have a No. 10 wire carrying 
24* amperes a distance of 90 feet at 110 volts, 24 X 
90=2160. Opposite No. 10 in the column marked 


B. & S. gauge 


and under 110 volts we find 529 


2160 
’ 529 


=4 and a very small fraction, which is the percent¬ 
age of loss occurring on this line. 

It is often necessary to reinforce mains which have 
become overloaded. It is quite usual though often 
very incorrect, to choose by the table of carrying 
capacities a wire of such size that the rated capacity 
of it and the wire to be re-enforced shall be equal to 
the load. Small wires have proportionately a much 
greater radiating surface than larger ones and there¬ 
fore their carrying capacity is proportionally great- 





282 


WIRING DIAGRAMS 


er. In order that a wire connected in parallel with 
another wire shall carry a certain current, its circular 


mils, must be equal 


C. M.Xa 
A 


where C. M. stands 


for the cross-section of the larger wire in circular 
mils and A for the current to be carried by it, while a 
is the current to be carried by the extra wire. Table 
No. 2 is calculated from this rule and shows the size 
of wire necessary to re-enforce another overloaded to 
a certain per cent, as indicated in the top row. For 
instance, a 0000 wire overloaded 40$ requires re-en¬ 
forcement by a No. 1; a No. 3 wire overloaded 20$ 
requires a No. 10 wire. Where large wires are re¬ 
enforced in this way by smaller ones great care must 
be taken that the larger wire cannot be accidentally 
broken or disconnected, since in such a case the whole 
load would be forced over the smaller wire and would 
likely result in a fire. The two wires should be secure¬ 
ly soldered together. 


No. 2. 


Am¬ 

peres. 

B. &S. 

10% 

20 

30 

40 

50 

60 

70 

80 

90 

100 

210 

0000 

6 

4 

2 

1 

0 

00 

000 

000 

0000 

0000 

177 

000 

8 

5 

3 

2 

1 

0 

00 

000 

000 

000 

150 

00 

9 

6 

4 

3 

2 

1 

0 

0 

00 

00 

127 

0 

10 

7 

5 

4 

3 

2 

1 

1 

0 

0 

107 

1 

10 

8 

6 

5 

4 

3 

2 

2 

1 

1 

90 

2 

11 

9 

7 

6 

5 

4 

3 

3 

2 

2 

76 

3 

12 

10 

8 

7 

6 

5 

4 

4 

3 

3 

65 

4 

14 

11 

9 

8 

7 

6 

5 

5 

4 

4 





























WIRING TABLES 


283 


No. 3. 


Numbers 

B. & S. 
Gauge. 

diameters 
in Mils. 

Areas in 
Circular 
Mils. 
C.M.=d 2 

0000 

460. 

211,600. 

000 

410. 

168,100. 

00 

365. 

133,225. 

0 

325. 

105,625. 

1 

289. 

83,521. 

2 

258. 

66,564. 

3 

229. 

52,441. 

4 

204. 

41,616. 

5 

182. 

33.124. 

6 

162. 

26,244. 

7 

144. 

20,736. 

8 

128. 

16,384. 

9 

114. 

12,996. 

10 

102. 

10,404. 

11 

91. 

8,281. 

12 

81. 

6,561. 

13 

72. 

5,184. 

14 

64. 

4,096. 

15 

57. 

3,249. • 

16 

51. 

2,601. 

17 

45. 

2,025. 

18 

40. 

1,600. 

19 

36. 

1,296. 

20 

32. 

1,024. 

21 

28.5 

812.3 

22 

25.3 

640.1 

23 

22.6 

510.8 - 

24 

20.1 

404. 

25 

17.9 

320.4 

26 

15.9 

252.8 

27 

14.2 

201.6 

28 

12.6 

158.8 

29 

11.3 

127.7 

30 

10. 

100. 

31 

8.9 

79.2 

J2 

8 

64. 

33 

7.1 

50.4 

34 

6.3 

39.7 

35 

5.6 

31.4 

36 

5. 

25. 


Weights. 

Ohms per 
1000 feet 

1000 

feet. 

Mile. 

641. 

3,382. 

.051 

509. 

2,687. 

.064 

403. 

2,129. 

.081 

320. 

1,688. 

.102 

253. 

1,335. 

.129 

202. 

1,064. 

.163 

159. 

838. 

.205 

126. 

665. 

.259 

100. 

529. 

.326 

79. 

419. 

.411 

63. 

331. 

.519 

50. 

262. 

.654 

39. 

208. 

.824 

32. 

166. 

1.040 

25. 

132. 

1.311 

20. 

105. 

1.653 

15.7 

83. 

2.084 

12.4 

65. 

2.628 

9.8 

52. 

3.314 

7.9 

42. 

4.179 

6.1 

32. 

5.269 

4.8 

25.6 

6.645 

3.9 

20.7 

8.617 

3.1 

16.4 

10.566 

2.5 

13. 

13.283 

1.9 

10.2 

16.85 

1.5 

8.2 

21.10 

1.2 

6.5 

26.70 

.97 

5.1 

33.67 

.77 

4. 

42.68 

.61 

3.2 

53.52 

.48 

2.5 

67.84 

.39 

2. 

84.49 

.3 

1.6 

107.3 

.24 

1.27 

136.2 

.19 

1.02 

168.5 

.15 

.81 

214.0 

.12 

.63 

271.7 

.095 

.5 

343.6 

.076 

,4 

431.6 




















































284 


WIRING DIAGRAMS 


No. 4. 

Table Showing the Currents Which will Fuse 
Wires of Different Substances. 


B. & S. 
Gauge. 

Diam. 

Copper. 

Aluminum. 

German 

Silver 

Iron. 

10 

102. 

333. 

246.5 

170. 

102.3 

12 

81. 

236. 

174.4 

120.5 

72.6 

14 

64. 

165.7 

122.8 

84.6 

50.9 

16 

51. 

117.7 

87.1 

60.1 

36.1 

18 

40. 

81.9 

60.7 

41.8 

25.2 

20 

32. 

58.5 

43.4 

29.9 

18. 

22 

25.3 

41.1 

30.5 

21.0 

12.4 

24 

20. 

28.9 

21.5 

14.8 

8.9 

26 

16. 

20.7 

15.3 

10.6 

6.4 

28 

12.6 

14.5 

10.7 

7.4 

4.5 

30 

10. 

10.2 

7.6 

5.2 

3.1 

32 

8. 

7.3 

5.4 

3.7 

2.3 

34 

6.3 

5.1 

3.8 

2.6 

1.6 

36 

5. 

3.6 

2.7 

1.8 

1.1 


















CHAPTER XXII. 


ELECTRIC SIGNS. FLASHERS. DISPLAY LIGHTING. 


Figure 198 gives a diagrammatic view of the 
Reynolds Flasher for electric signs and displays. The 
flasher here shown is capable of controlling twelve 
circuits, each circuit with a single-pole switch. Only 



FIGURE 198. 


one wire of each circuit passes through the flasher and 
single-pole fuses are usually installed as near as pos¬ 
sible to the flasher. The fuses for the other sides of 
the circuits may be installed within signs or wher¬ 
ever convenient. The diagram shows flasher ar- 

285 


































































































286 


WIRING DIAGRAMS 


ranged for three-wire circuits. In case of a two-wire 
installation only one of the mains is led to the flasher 
and the two sections of the flasher are connected to- 

Figures 199 to 204 show the circuits of a flasher 
for electric signs and displays made by Rawson 
& Evans of Chicago. This machine is designed 
to change connections from one circuit to another 
without ever entirely opening the circuit. From two 




redH 
—6 - 


WHITEST 
-=? - 


GREEN jQ_2_ 


Sfe: 


FIGURE 199. 


to four groups of lamps are wired in series and tne 
movable arms, A, B, C, Figure 199, short-circuit 
those groups not in use. During the time of change 
from one group to another all the groups are in 
series and most of the current which would otherwise 
manifest itself in the form of a spark passes through 
the lamps. The time of open circuit is so very short 
that it is impossible to hold an arc for any appre¬ 
ciable time. The breaking of the circuit in many 
places at the same time also lessens the destructive 
qualities of the arc which occurs. 






























ELECTRIC SIGNS 


287 


Figure 199 is a diagram of the flasher as connect¬ 
ed to three-color signs; the white lights being ar¬ 
ranged to follow after the red and also after the 
green. Referring to Figure 199, A, B, C, are metal 
arms insulated from one another but firmly fastened 
^together so as to form one movable piece. As these 
arms are moved from point to point they connect 
the diametrically opposite terminals, 1, 1'; 2 , 2'; 
3, 3'; and 4, 4'. In Figure 199 the current passes 
along wire 5 through the red lights connected to cut¬ 
out X, to wire 6, point 2 \ arm B to point 2 , thence 
to point 4 r , arm A, points 4 and 3 to arm C, back to 
the other pole of dynamo. So long as the arms re¬ 
main in this position the r 1 lights burn and all the 
others are short-circuited. The next position of the 
machine brings arm A in contact with points 1 and 
l' ; current now passes direct from point 1 through 
arm A to point 1', wire 6 and the white lights at Y; 
arm A now forming a short circuit around the red 


lights. The current passing through the white lights 
returns over wire 7 to point 3 and arm B (which has 
also moved) to the other pole of dynamo. The white 
lights now burn and all others are short-circuited. 

The next movement brings arm A in contact with 


points 2 and 2 ' and C to 1 and 1', leaving no con¬ 
nection between 3 and 3'. The current now passes 
through arm C from point 1 to 1'; thence to point 
arm A, point 2 , 4' arm B to point 4 through the 
green lights and back to point 3' and to the other 


288 


WIRING DIAGRAMS 


pole of the dynamo. The green lights now burr 
while the others are short-circuited. 

The fourth position of the arms leaves the space 
between 4 and 4' open and the current again passes 
through one of the arms from point 1 to 1', wire 6, 
white lights, wire 7 to points 3, 3' and back to dyna¬ 
mo. An elementary diagram of those connections is 
shown in Figure 200. Three of the points, 1, 2, 3, 4, 
are always short-circuited. 



Figure $01 shows the same machine with one of the 
arms removed connected to control a double-face sign, 
one side to bum at a time. The current in this case 
passes from the positive pole of the switch to the 
upper group of cutouts which represent one side of 
the sign. The current passing through these lamps 
continues to point 2 r , thence to point 1, arm A, point 
1' and 3, arm B and negative pole of the switch. The 
next movement brings arm B in contact with point 4' 
and current passes along it to 4, thence to 2, arm 
A to 2', the lower group of cutouts representing the 















ELECTRIC SIGNS 289 


other side of sign and back to the negative side of 
the switch. 



Figure 202 shows connections for four groups of 
colors, one at a time being illuminated. 

In Figures 203 and 204 connections for single and 
double-pole break are shown. 



--— 

o 1® — 
Oj <* — 


s- 

•ol c 

O Q 






o fa 

2H 






LJ 


FIGURE 202. 

For large installations, in connection with three- 
wire systems, double-disc machines are used; the posi¬ 
tive and neutral wire connecting to one and the nega¬ 
tive and neutral to the other. 





































































290 


WIRING DIAGRAMS 


This machine and the combination of circuits are 
protected by letters patent. 


cn 

I <V 


•0 




0 


1 ° f 


JJ TLVMA I Q 

— § #- 


FIGURE 203. 


FIGURE 204. 


Figure 205 will serve to illustrate the principle of 
several of the monogram signs. The incandescent 
lamps L are each set within a metal shield which pre¬ 



vents the spread of light to any other part of the 
sign. One common feed wire leads to all of the 
lamps, and from each lamp a switch wire leads to the 
machine serving to make the proper connections. 
Each monogram has the lights within it so distrib¬ 
uted that by lighting the proper lamps any letter in 
the alphabet can he made and a sign, consisting, say. 

















































ELECTRIC SIGNS 


291 


of 10 monograms, can, therefore, be made to spell 
out any word or combination of words which does not 
exceed ten letters. 



The mechanism used for spelling out words consists 
of a set of discs for each monogram and these carry 
brass bars, as shown at B, which serve to energize 


WATCH FOR 
Electric No. 

600 


DriYers' (ft 


•'CB 

lUva 


M 

o 

w 

§ 

o 


O 

o§ 

M 

< 

u 


DONT FOLD THIS CARD 

eiTIMUD ,^7 

o^> 


'O O- 

*€) 


oo 

QQ 


o 

Q. 


"GlVETHIS CHECK TO ON-FOeMEO ATTENWNTOhL^ 

Leased from Ttl® ElSCtfiC C«li8g« CjllC*. 


the wires leading to the lamps. These bars are cut 
out as shown and only those sections remaining full 
make contact with the switch wires. 

Figure 206 is a representation of a monogram used 


































292 


WIRING DIAGRAMS 


as a carriage call, principally for theatres. In this 
case only nine wires are used for each monogram and 
in case the sign is illuminated on both sides each of 
the nine wires supplies two monograms, one on each 
side. One wire is a common feed for all of the lamps 
and the other eight wires serve each to connect a 
small group of lamps in the monogram. These 
groups of lamps are so arranged that by a combina¬ 
tion of them almost any number from 0 to 9 can be 
made. To accomplish this a perforated card shown 
at bottom of this cut is used. The card shown is 
arranged for a sign consisting of three monograms. 

As will be seen the yoke Y carries 8 contact points 
each of which is capable of making contact and ener¬ 
gizing the wire connected to it when the yoke is 
pressed down upon the current carrying bar beneath 
it. In order to allow none but the proper points to 
be connected the card is inserted between the current 
carrying bar and the yoke. Thus the figure 6 is 
made by allowing only the points 1, 2, 5 and 7 on 
the yoke to make connection with the bar below. The 
0 is formed by making connection with points 1, 4, 

5 and 7. In this figure all of the lamps denoted by 
the same number are on one circuit. The lamps marked 
% if lighted, will form the figure 1; the lamps 1, 4, 

6 and 7 form the figure 6, while 0 is formed by 1, 4, 
6 and 8. 

A somewhat similar monogram is made by wiring 
the necessary number of properly distributed lamps 


ELECTRIC SIGNS 


293 


on one or more circuits in the usual manner and then 
inserting lamps only where required to outline the 
letter or number wanted, the other openings being cov¬ 
ered. 

All of these devices are covered by letters patent* 
The information herein given is intended merely to 
enable wiremen to intelligently go about connecting 
them should occasion require. 



INDEX 


Absorption of light, 276. 

Alternating current generator, 182. 

Alternating current motor, 196. 

Annunciator circuits, 21. 
telephone, 47. 

Arc-circuits, 105. 
dynamo, 167. 
lamps, A. C., 117. 
lamps, D. C., 116. 
switchboard, 236. 

Armatures, 233. 

Arresters, lightning, 49. 

Automatic cutout, gas lighting, 65. 

Automobiles, 159. 

Auto-starter, 212. 

Auto-transformer, 198. 

Battery, dry, 69. 
grouping of, 66. 
resistance of, 72. 
secondary, 71. 

*e»e of, 84. 

.ret, 68. 

Bell circuits, 7. 
control of, 11. 
differential, 14. 
on dynamo circuit, 16. 
polarized, 16. 
short-circuit, 14. 
single stroke, 15. 

Booster, 250. 

Bridging system, telephones, 44. 

Brush arc lamp, 116. 
armature, 234. 

Bunsen photometer, 276. 

Burglar alarms, 28. 

Callow’s constant ringing attach¬ 
ment, 34. 


Candle-power, test for, 276. 
Capacity, 230. 

Carbons, consumption cf, 275. 
Cascade connection for motors, 206w 
Charging circuits for automobiles 
163. 

storage batteries, 18, 250. 

Circle, area of, 95. 

Circular mills, 95. 

Circumference of circle, 95. 
Compensator, D. C., 177. 
alternating current, 198. 
in parallel, 180. 

Compound wound dynamo, 170. 

motor, 134. 

Condenser, 89. 

action of, 226. 

Connecting bell circuits, 76. 

incandescent circuits, 231. 
Continuous ringing attachments, 15 , 
Controller, motor, 152. 

A. C. motor, 211. 

Convertible system, 98, 108. 
Cooper-Hewitt lamp, 122. 

Copper wire, dimensions of, 283. 
resistance of, 96. 
weight of, 95. 

Counter E. M. F., 229. 

Cumulative winding, 134. 

Current, induced, 58. 

Differential bell, 14. 

winding on motor, 134. 

Direction of current, 86, 90. 
Discount meter, 129. 

Divided circuits, 92. 

Door opener, 7. 

Drum armature, 185, 233. 

Dynamo current for bells, 16 , 38 . 




INDEX 


Dynamo, A. C., single-phase, 182. 
arc, 177. 

compound wound, 170. 
series wound, 167. 
shunt wound, 168. 

Edward’s condenser system, 63. 
Electric signs, 285. 

Electrolytic interrupter, 60. 

Elevator controller, A. C. motor, 
216. 

signals, 113. 

End cell switch, 250. 

Equalizer, 174. 

Fire alarm system, 28. 

Flashers for electric signs, 285. 

Fort Wayne single-phase motor, 204. 
Frequency meter, 222. 

Fusing currents, 284. 

Gas lighting circuits, 61. 

Generator, monocyclic, 187. 
single-phase, 185. 
three-phase, 190. 
three-wire, 182. 

Gramme ring armature, 229. 

Ground connections, 7. 
detectors, D. C., 243. 
detectors, A. C., 247. 

Incandescent light circuits, 97. 
lamps as resistance, 17, 165. 
lamps, efficiency of, 273. 
lamps, wattage of, 263. 

Induction coil, 58, 89. 

Induction motor, 196. 
Intercommunicating telephone, 45. 
Interrupter, current, 59. 

Iron wire, resistance of, 96. 
weight of, 96. 

Joints in wires, 278. 

Jump spark, 163. 

Light, intensity of, 273. 

Lines of force, 86. 

Long shunt, 171. 

Losses, on wires, 277. 

on three-wire system, 176. 

Magnetism, 94. 


Magneto, testing with, 263. 

Monocyclic generator, 187. 

Monogram letter, 290. 

Motor, compound wound, 134. 
direct current, 131. 
reversing, A. C., 197. 
reversing, D. C., 135. 
series wound, 131. 
shunt wound, 133. 
single-phase, 201. 
synchronous, 196. 
three-phase, 199. 

Nernst lamp, 121. 

Neutral wire, 176. 

Ohm’s law, 91. 

Organ controller, 143. 

Over-compounding, 171. 

Overload starting box, 137. 

Parallel wires in, 281. 
dynamos in, 171, 191. 

Partrick, Carter & Wilkins annun<™« 
ator system, 25. 

Photometer, 276. 

Polarized bell, 16. 

Power factor, 231. 

Power factor meter, 222. 

Printing press controller, 139, 144 
152. 

Pump motor controller, 141. 

Rawson & Evans Flasher, 286. 

Recording wattmeters, 125. 

Rectifier, mercury arc, 256. 

Reinforcing wires, 125. 

Remote control, 107. 

Repeater, telegraph, 50. 

Resistance of batteries, 72. 

Return call annunciators, 24. 
bell circuits, 7. 

Self induction, 229. 

Separate exciter, 195. 

Series arc circuit, 110. 
arc dynamo, 167. 
incandescent circuit, 109. 
motors for constant current, 150. 
motors for constant potential, 131. 






INDEX 


Short-circuit bell, 14. 

Short-circuits on bell systems, 83. 

test for, 259. 

Short shunt, 171. 

Shunt motor, 133. 

multiplying power of, 93. 
dynamo, 168. 

Signs, electric, 285. 

Single-phase armature, 234. 
dynamo, 182. 
motor, 201. 

Single stroke bell, 15. 

Split phase motors, 203. 

Starting, A. C. motors, 198. 
box, 137. 

switch, A. C. motors, 209. 

Storage batteries, 71. 

circuits for automobiles, 150. 
connections, 250. 

Street car motor circuit, 147. 
Switchboard, arc, 236. 
direct current, 240. 
theater, 112. 

Synchronous motor, 196. 
Synchroscopes, 191, 220. 

Tandem connection fo» motors, 206. 
Teaser wire, 187. 

Telautograph, 52. 

Telegraph circuits, 49. 

repeaters, 60. 

Tf4ephone circuits, 43. 

£«st for insulation resistance, 84. 


Testing board, A. C., 220. 

Testing incandescent circuits, 259. 

T.-H. arc switchboard, 238. 
armature, 234. 

Theater switchboard, 112. 

Three-phase armature, 235. 
system, lights on, 100. 

Three-wire generator, 182, 190. 
system, 97. 

Transferring arc circuits, 236. 

Transformers, 226. 

Tree system, 97. 

Trouble, locating on bell systems, 79 

Underload starting box, 137. 

Voltmeter connections, 243. 
testing with, 263. 
formula for test, 265. 

Wagner single-phase motor, 201. 

Watts, definition of, 94. 

Wattage of incandescent lamps, 273. 

Wattless current, 231. 

Wattmeter, recording, 125. 

Western Electric Co. arc dynamo* 
167. 

Wheatstone bridge, 266, 270. 
test with, 263. 

Wiring tables, 277. 

Wright discount meter, 199. 

X-nr, 57. 



DIRECT 

AND ALTERNATING 
CURRENT MOTORS 







. 







•i 













CONTENTS 

Page 

Chapter I 

Direct-Current Electrical Circuits. 9 

• Chapter II 

Magnetism, Electromagnetism, Magnetic Circuit, and Elec¬ 
tromagnetic Induction . 25 

Chapter III 

Alternating-Current Electrical Circuits. 40 

Chapter IV 

Electrical Measurements . 56 

Chapter Y 

Armature Windings for Direct-Current Motors. 68 

Chapter VI 

Commercial Types of Direct-Current Motors. 80 

Chapter VII 

Speed Control, Operating Characteristics, and Testing of 
Direct-Current Motors .124 

Chapter VIII 

Care and Operation of Direct-Current Motors and Direct- 
Current Motor Troubles.146 

Chapter IX 

Armature Windings for Alternating-Current Motors.157 

Chapter X 

Commercial Types of Alternating-Current Motors.171 

Chapter XI 

Speed Control, Methods of Starting, and Operating Charac¬ 
teristics of Alternating-Current Motors.204 

Chapter XII 

Care and Operation of Alternating-Current Motors and Al¬ 
ternating-Current Motor Troubles.222 

Appendix .229 

Index.233 

7 


















ELECTRIC MOTORS 


CHAPTER I 

DIRECT-CURRENT ELECTRICAL CIRCUITS 

Electrical Circuit .—The path in which electricity 
moves is called the electncal circuit, and it is neces¬ 
sary to have a working knowledge of the various prop¬ 
erties of electrical circuits and the quantities asso¬ 
ciated with them in order to completely understand 
the operation of electrical machinery. Electrical cir¬ 



cuits are of numerous forms, but all possess to a great 
degree the same properties and involve the same 
quantities. Suppose, for example, a small electric 
motor is operated from a storage battery, as shown 
in Figure 1. This combination constitutes an elec¬ 
trical circuit which is typical of all electrical cir¬ 
cuits. It contains a source of electrical energy—the 
battery; an energy transforming device—the electric 

9 












10 


ELECTRIC MOTORS 


motor ; and the necessary connecting material—wires 
and switch. It must be remembered that all electrical 
circuits are closed on themselves and, like the cir¬ 
cumference of a circle, have neither beginning 
nor end. 

Current of Electricity. —The flow of electricity can 
be compared to the flow of water in a pipe. The flow 
of water is usually expressed as so many gallons per 
minute, so many cubic feet per minute, or any combi¬ 
nation of volume and time. The flow of electricity 
is likewise expressed as so many units of quantity 
in a unit of time. The unit of quantity of electricity 
is called the coulomb. When there is a uniform flow 
of one coulomb through the circuit each second, there 
is said to be a unit of current of electricity in the 
circuit. A flow of one coulomb per second is called 
an ampere. 

Resistance of Electrical Circuit. —The opposition 
offered by a circuit to the free flow of electricity 
through it is called the resistance of the circuit, and 
it is measured in a unit called the ohm. The resist¬ 
ance offered by different materials to the flow of 
electricity through them varies between wide limits. 
Those materials which offer a relatively low resistance, 
such as the metals, are called conductors ; while those 
materials which offer a relatively high resistance, such 
as glass, rubber, dry paper, etc., are called insulators. 

Electrical Pressure. —The electrical pressure—some¬ 
times called the electromotive force, electricity moving 
force , voltage , or drop in potential —causes the elec¬ 
tricity to move in the electrical circuit when the cir¬ 
cuit is closed, and it is measured in a unit called the 
volt. There are a number,of ways of producing an 
electrical pressure, but the two most common are by 


DIRECT-CURRENT ELECTRICAL CIRCUITS 


11 


chemical action in the battery, and by electromagnetic 
induction in the generator. 

Ohm’s Laic for Electrical Circuit. —Dr. G. S. Ohm 
experimentally discovered that there was a definite 
relation between the resistance of a circuit, the pres¬ 
sure acting on the circuit, and the current produced. 
The values of the units in which resistance, pressure, 
and current are measured are such that the relation 
may be written as follows: 

volts 

amperes =- 

ohms 


The current in amperes, the pressure in volts, and 
the resistance in ohms are represented by the symbols 
l, E, and R, respectively. Substituting these symbols 
for the quantities in the above equation gives 

'i.<*> 


Other forms in which the above equation may be 

Written are as follov r s: 

, volts 

ohms =-■ 

amperes 

R = j .(b) 


and 


volts = amperes x ohms 

E = IxR .(c) 


Examples.— 1 . The field winding of a direct-current motor 
has a resistance, under operating conditions, of 30 ohms. \\ hat 
is the value of the field current when the impressed pressure 

is 110 volts? 







12 


ELECTRIC MOTORS 


Solution .—Substituting the values of pressure and resistance 
in equation (a) gives 



= 3.67— amperes 

2. What resistance must an electrical heater have in order 
that it may take a current of 5 amperes from a 220-volt circuit? 

Solution .—Substituting the values of current and pressure in 
equation (b) gives 



= 44 ohms 

Ohm’s law holds true for any part of a circuit just 
the same as it does for the entire circuit; that is, the 
pressure over any part of the resistance of a circuit 
is equal to the product of the resistance of that portion 
of the circuit and the current. 

Calculation of Resistance. —The resistance of a con¬ 
ductor varies directly as the length and inversely as 
the area of the conductor; that is, the longer the con¬ 
ductor the greater the resistance and the larger the 
conductor the smaller the resistance. The resistance 
of a conductor also depends upon the kind of material 
of which it is composed. The above relations may 
be put into the form of an equation as follows: 

. , constant x length 

resistance =- 

area 

Representing the constant in the above equation by 
K , the length by l, and the area by A, the equation 
may be written as follows: 

B=K- 

A 





DIRECT-CURRENT ELECTRICAL CIRCUITS 


13 


The value of the constant K will depend upon the 
kind of material in the conductor and also upon the 
units in which the value of the length and the area 
of the conductor are measured. When the length is 
measured in feet and the area in circular mils, the 
value of K is called the mil-foot resistance of the 
material. The area of a conductor in circulai mils 
is equal to the diameter of the conductor in mils 
multiplied by itself. The mil is equal to the one- 
thousandth part of one inch. If the area of a con¬ 
ductor in circular mils is known, its area in square 
mils can be computed by multiplying the value of the 
circular-mil area by .7854. To change an area in 
square mils to circular mils divide by .7854. The 
area of a rectangular conductor in square mils is equal 
to its area in square inches multiplied by 1,000,000. 
The values of the mil-foot resistance for some of the 
more common metals are given in Table I in the 

Appendix. 

Example.— Calculate the resistance of a conductor 500 feet 
■Jong, having a diameter of 102 mils and composed of a material 

having a mil-foot resistance of 10.8. . 

Solution. — Substituting directly in the equation for resistance 

gives 

10.8 X 500 
B ~~ 102 X 102 


5,400 
= 10,404 
= .519 + ohm 

The majority of electrical conductors are circular 
in cross-section and they are drawn to certain definite 
sizes. The diameter, area in circular mils, resistance, 




14 


ELECTRIC MOTORS 


etc., for different size copper wires are given in Table 
II in the Appendix. 

Resistance Changes with Temperature .—The resist¬ 
ance of practically all substances changes when there 
is a change in their temperature. Almost all mate¬ 
rials increase in resistance with an increase in tem¬ 
perature, the resistance of some, however, decreases 
with rise of temperature. The carbon filament lamp 
when hot has about one-half the resistance it has when 
cold. Some alloys, such as manganin, experience prac¬ 
tically no change in resistance due to change in 
temperature. 

The change in resistance of a material per ohm due 
to a change in temperature of one degree is called 
the temperature coefficient of the material. Thus, 
if a copper wire had a resistance of 10 ohms at 32 
degrees Fahrenheit and 10.233 ohms at 42 degrees 
Fahrenheit, its temperature coefficient wrnuld be cal¬ 
culated as follows: The total change in resistance is 
equal to 10.233-10, or .233 ohm. This change in 
resistance is due to a change in temperature of 10 
degrees; hence, the change per each degree is one- 
tenth of this amount, or .0233. This increase of .0233 
ohm per degree occurs in 10 ohms, then the change 
per ohm will be equal to one-tenth of this, or .00233. 
Hence, the temperature coefficient of the material 
based on 32 degrees Fahrenheit is equal to .00233. 
The values of the temperature coefficients for some of 
the more common materials are given in Table I in the 
Appendix. These values are all based on an initial 
temperature of zero degrees centigrade and 32 degrees 
Fahrenheit, and, if the initial temperature of the 
conductor does not correspond to these values, its 
resistance at the freezing temperature should be cal- 


DIRECT-CURRENT ELECTRICAL CIRCUITS 15 

culated first; and another calculation should be made 
to determine its resistance at the second temperature. 

Example. —The shunt field coil of a motor has a resistance 
of 53.5 ohms at 62 degrees Fahrenheit, what will its resistance 
be at 90 degrees? 

Solution. —One ohm at 32 degrees, if raised to a temperature 
of 62 degrees, will increase in resistance .00233 ohm for each 
degree rise in temperature, or the total increase for each ohm, 
in this case, will be equal to .00233 X 30, or .0699. Then the 
one ohm at 32 degrees will have 1.0000 + .0699, or 1.0699 ohms 
at 62 degrees. Since the total resistance at 62 degrees is 53.5 
ohms, the resistance at 32 degrees will be equal to 53.5 — 1.0699, 
or 50 ohms. The increase in resistance of each ohm when the 
temperature rises from 32 degrees to 90 will be .00233 X 58, 
or .13514; and the resistance of each ohm at 90 degrees will 
be 1.00000 + .13514, or 1.13514. The resistance of 50 ohms 
at 32 degrees will be equal to 50 X 1.13514, or 56.75 ohms, 
at 90 degrees. 

Series Circuits. —A series circuit is one in which 
the various elements constituting the circuit are so 
connected that there is only one path in which the 
electricity can flow. For example, in Figure 2, two 
resistances R ± and R 2 and tw T o dry cells are all con¬ 
nected in series. The total resistance of such a circuit 
is equal to the sum of the resistances of the different 
parts of the circuit. 

The effective pressure acting in such a circuit as 
that shown in Figure 2 is equal to the sum of the 
different pressures provided they are all connected 
so as to act in the same direction. The terminal of a 
source of electrical pressure from which the current 
flows is called the positive or plus terminal and is 
always marked in a diagram by means of the sign of 
addition (+) ; while the terminal toward which the 
current flows is called the negative or minus terminal 
and is marked in a diagram by means of the sign of 


16 


ELECTRIC MOTORS 


subtraction (-). In the case of the dry cell, the posi¬ 
tive terminal is the carbon rod and the negative ter¬ 
minal is the zinc cup, and each is provided with a con¬ 
venient binding post for making connections. If a 
number of sources of electrical pressure be connected 
in series, but in such a way that some of them tend 
to produce a current through the circuit in one direc¬ 
tion and the others in the opposite direction, then the 



Figure 2.—Series Electrical Circuit. 

effective pressure will be equal to the difference be¬ 
tween the combined pressures in one direction and the 
combined pressures in the opposite direction, and the 
direction of the current will be determined by the 
difference in the combined pressures. 

Example .—Six dry cells, each having an electromotive force 
of 1.5 volts and an internal resistance of .05 ohm, are con¬ 
nected in series, the positive terminal of one being joined to 
the negative terminal of the next, etc. This combination of 
cells is connected to a circuit composed of two coils of wire 
having resistances of 1 and 3 ohms, respectively, and the con¬ 
necting leads have a resistance of .2 ohm. What current will be 
produced? 

Solution .—The total internal resistance of the dry cells will be 
equal to 


6 X .05 = .3 ohm 










DIRECT-CURRENT ELECTRICAL CIRCUITS 17 

The total resistance of the circuit, ■which we will represent by 
B, will be equal to 

B = .3 + 1.0 + 3.0 + .2 
= 4.5 ohms 

The effective pressure acting in the circuit, which we will repre¬ 
sent by E, will be equal to the combined pressure of the six 
cells, since they all tend to produce a current in the same direc¬ 
tion through the circuit, or 

E = 6 X 1.5 
= 9 volts 

Substituting these values of resistance and pressure 
in equation (a) under Ohm’s law gives 



4.5 

= 2 amperes 

If two of the cells in the above problem were con¬ 
nected so that their pressures opposed the pressure of 
the remaining four, then the effective pressure would 
be obtained as follows: 

E= (4x1.5) - (2x1.5) 

= 6-3 
= 3 volts 

Parallel or Divided Circuits .—A parallel, or di¬ 
vided circuit is one in which there are two or more 
paths’ provided for the current. For example, the 
three resistances R„ R., and R 3 , Figure 3 are con¬ 
nected in parallel between the terminals of the two 
dry cells. There are three paths for the total current, 
and the currents in the different paths will be to 
each other inversely as the resistances of the different 
paths That is, if one path is twice the resistance ot 


18 


ELECTRIC MOTORS 


another, it will carry only one-half as much current 
as the other path. 

The reciprocal of a resistance; that is, one divided 
by the resistance, is called its conductance. Repre¬ 
senting the combined resistance of a number of re- 



Figure 3.—Parallel Electrical Circuit. 


sistances in parallel by R, then the conductance will 
be equal to (1 +R). The total conductance of a paral¬ 
lel circuit is equal to the sum of the conductances of 
the several parts, 


_1_ J_ JL _L 

R R 1 R % R % 

The two dry cells in Figure 3 are connected in 
parallel, and the pressure of the combination is the 
same as that of a single cell, assuming their pressures 
and internal resistance are equal. 

Example .—The three resistance 2?,, R 2 , and 2? s , Figure 3, are 
10, 4, and 20 ohms, respectively. Each dry cell has an electro¬ 
motive force of 1.3 volts and an internal resistance of .1 ohm, 
Determine the total current produced by the two cells, the 



















DIRECT-CURRENT ELECTRICAL CIRCUITS 19 

current in each cell, also the current in each of the three 
resistances. 

Solution .—Substituting in the above equation for the com¬ 
bined conductances gives 

JL_ 1,1.1 = ! = i 

R 10 '4 ^20 20 5 

1_ 4 

R 5 


= 1.25 ohms 

The total internal resistance of the two cells in parallel is cal¬ 
culated in a manner similar to the above, or, representing the 
total internal resistance by r, we have 



10 10 
= 20 


since 


then 


01 


r ~~ 20 

= .05 ohm 

The total resistance of the entire circuit is equal to 

1.25 + .05 = 1.3 ohms 

Since the effective pressure is 1.3 volts, we obtain the total 
current by substituting in equation (a) under Ohm s law, 

which gives 

J- .O 

L3 


= 1 ampere 


20 


ELECTRIC MOTORS 


This total current divides equally between the two dry cells, 
since their electromotive forces and internal resistances are 
equal in value or there will be a current of one-half ampere 
in each cell. 

The currents in the 4-, 10-, and 20-ohm resistances will be to 
each other as 20, 8 and 4, or as 5, 2, and 1 are to each 
ether. The 4-ohm coil will carry five-eighths of the total cur¬ 
rent; the 10-ohm coil, two-eighths; and the 20-ohm coil, 
one-eighth. 

Electrical Work or Energy .—Work is the result of 
a force acting through a certain distance. For exam¬ 
ple, if a force of 100 pounds is required to raise a 
body through a vertical distance of 10 feet, there will 
be 100x10, or 1000 foot-pounds of work done. A 
force may exist without doing work; as, for example, 
you may shove against a wall with a certain force, 
yet you will do no work unless there is a movement 
of the wall. Thus, a generator may be operating 
and generating an electrical force, but it is not suffi¬ 
cient to overcome the resistance between the termi¬ 
nals of the machine, therefore, no current is produced 
and the generator is not doing any work. If, however, 
a conductor be connected to the terminals of the 
generator, a current will be produced by the electrical 
force and, as a result, the generator will do work. 
The electrical work done by the generator in produc¬ 
ing the current will manifest itself as heat and cause 
the conductor to become heated. 

Energy, in general, is the capacity or ability to do 
work and it is measured in the same unit as work, 
since it is numerically equal to the work done. Thus 
the energy possessed by a certain quantity of elec¬ 
tricity at a certain electrical level, with respect to 
its energy at some other electrical level, is equal to 
the work done on or by the quantity in moving from 


21 


DIRECT-CURRENT ELECTRICAL CIRCUITS 


the first to the second electrical level. If the elec¬ 
tricity moves from a higher to a lower level, it gives 
up energy or does work; while, if it moves from 
a lower to a higher level, work is performed and 
the energy possessed by the electricity is increased. 

The unit of electrical work or energy is called the 
joule , and it is numerically equal to the work done m 
raising one coulomb of electricity through a difference 
in electrical level of one volt. The value of the 
work done in performing a given operation is inde¬ 
pendent of the time required. For example, it will 
require the same amount of work to raise a certain 
weight a given height in 10 minutes as would be re¬ 
quired to raise it the same height in 1 hour. The elec¬ 
trical work W done in moving a certain quantity ot 
electricity Q through a difference in electrical level of 
E volts may be determined by the following equation; 


W = E x Q 


The quantity of electricity Q is equal to the prod¬ 
uct of the steady current in amperes times the time 
in seconds; and the work, in joules, done m a given 
time may be determined by the following equation: 

joules = volts x amperes x time (in seconds) 

W = ExIxt 


Mechanical and Electrical Power.— Power is nu- 
merically equal to the rate of doing work, or the rate 
at which energy is expended. If mechanical work 
is being performed by a machine, such as a motor 
at the rate of 33,000 foot-pounds per minute or ooO 
foot-pounds per second, the machine is said to be 
developing 1 horsepower. The horsepower of a 


22 


ELECTRIC MOTORS 


machine, lip., may be determined by the following 
equation: 


horsepower = 


work in foot-pounds 
33,000 x time (in minutes) 


or 



_ W _ 

33,000 x time (in minutes) 


If the time is expressed in seconds in the above 
equation, then the constant 33,000 should be changed 
to 550. When electrical work is being done at the 
rate of one joule each second, the power developed is 
called a watt. 


Power (in watts) = 


joules 

time (in seconds) 


P = 


volts x amperes x time 
time 


P = volts x amperes 
P-Exl watts 


One watt is equal to .7373 foot-pounds per second, 
or one foot-pound per minute is equal to 1.356 watts. 
Since one horsepower is equal to 550 foot-pounds per 
second, an electrical equivalent rate of doing work 
would be 

550 -f .7373 = 746 watts 

= 1 electrical horsepower 

Hence, to change mechanical horsepower to electrical 
units, multiply by 746, or 


watts = horsepower x 746 






23 


DIRECT-CURRENT ELECTRICAL CIRCUITS 


To change power in watts to horsepower, divide by 
746, or 

horsepower = watts -5-746 

From the above discussion, it is readily seen that 
the electrical work or energy in joules is equal to the 
product of the power in watts times the time m sec¬ 
onds. The joule, however, is too small a unit for the 
majority of practical purposes, and, for this reason, 
larger units are generally employed. These larger 
units are merely a combination of a power and time 
unit as given below. 


watt-hours = watts x hours 
kilowatt-hours = kilowatts x hours 


The kilowatt is equal to 1000 watts. The watt-hour 
meters used by the central station and power com¬ 
panies usually record the energy supplied to the con¬ 
sumer for lighting or power purposes in watt-hours 
or kilowatt-hours. Quite frequently the dials of these 
meters are not direct reading and their indication 
must be multiplied by a definite constant or factor, 
usually marked on the meter, m order to obtain the 

true value of the energy. 


Example .—A 110-volt direct-current motor is operating under 
«uch a load that it draws 75 amperes from the 110 -volt circuit 
to which it is connected. Determine the power input to this 
motor in watts, kilowatts, and horsepower; also the cost of 
energy to operate it for 10 hours if you have to pay 4 cents 

Tier kilowatt-hour for the eneigy. _ ... •. 

P Solution .—The power input to the motor m watts wi 

equal to the product of current and voltage, or 


P = 75 X HO 


= 8250 watts 


24 


ELECTRIC MOTORS 


Dividing the input in watts by 1000 gives input in kilowatts, or 

P = 8250 -- 1000 
= 8.25 kilowatts 

To change the input in watts to horsepower, divide by 746, 
which is the number of watts in 1 horsepower. 

P = 8250 746 

= 11.06 horsepower 

The total energy input to the motor in kilowatt-hours for a 
period of 10 hours will be equal to the product of the power in 
kilowatts and the time in hours, or 

8.25 X 10 = 82.5 kilowatt-hours 

The cost of this energy at .04 dollar per kilowatt-hour will be 

82.5 X .04 = 3.30 dollars 


CHAPTER II 


MAGNETISM, ELECTROMAGNETISM, MAGNETIC CIR¬ 
CUIT, AND ELECTROMAGNETIC INDUCTION 

Magnetism and the Magnet —Any body which, 
when freely suspended or supported, assumes an ap¬ 
proximately north and south position is called a mag¬ 
net, and the property of the body causing it to assume 
this position is called magnetism. A natural magnet 
is a body possessing magnetic properties as found m 
nature; while an artificial magnet is a body possessing 
magnetic properties after some special treatment, such 
as placing it in contact with or under the influence ot 
a natural or artificial magnet, or under the magnetiz¬ 
ing influence of an electric current. 

Any substance which is attracted by a magnet is 
called a magnetic substance. The most common mag¬ 
netic substances are iron and steel, although cobalt 
and nickel are attracted to a slight extent by a strong 

Magnetic Poles .—The end of a magnet which points 
approximately north, when the magnet is supported 
so that it is free to turn in a horizontal plane is called 
the north-seeking, or north-pole, and is usually desig¬ 
nated by N. The other end of the magnet is called the 
south-seeking, or south pole, and is usually designated 

^If the like poles of two magnets be presented to 

25 


26 


ELECTRIC MOTORS 


each other, it will be observed that there is a force 
of repulsion between them; while, if the unlike poles 
of two magnets be presented to each other, it w T ill be 
observed that there is a force of attraction between 
them. The results just stated may be summarized 
in a general law, as follows: Like magnetic poles repel 
each other, and unlike magnetic poles attract each 
other. 

Magnetic Field. —A magnetic field is any region 
where there will be a magnetic force acting on a mag¬ 
netic substance if the substance be introduced into 
this region. All magnetic fields have two properties: 
direction and strength; and it is necessary to know 
both in order to completely define the field. If a bar 
magnet be placed directly under a piece of heavy 
writing paper and some fine iron filings sprinkled 
on the paper, at the same time slightly jarring it, the 
filings will arrange themselves in rather regular curves 
extending from one end of the magnet to the other. 
It will be observed, as you trace these curves from 
one end of the magnet, that they separate until you 
reach the center of the magnet, when they start to 
approach each other and continue to do so until you 
reach the other end. These, curves in which the iron 
filings arrange themselves correspond in direction to 
what are called lines of magnetic force. The positive 
direction of these lines of force is taken as the direc¬ 
tion in which the north pole of a compass needle will 
point when placed in the magnetic field. They all 
originate at the north pole of the magnet, pass through 
the surrounding space, and terminate at the south 
pole; and their direction at any point corresponds 
to the direction of the magnetic field at that point. 
The number of these imaginary lines of force which 


MAGNETISM, ELECTROMAGNETISM 


27 


pass through a unit of area perpendicular to their 
direction is a representation of the strength of the 
magnetic field. The total number of fines which are 
supposed to terminate at the magnetic pole will de¬ 
pend upon the total strength of the pole. 

Magnetic Field Produced by a Current .—If a com¬ 
pass needle he placed beneath a conductor in which 
there is no current, the compass needle will come to 
rest in an approximately north and south position. 
The position of the compass needle will change, how¬ 
ever, when a current is produced in the conductor, 
due to there being a magnetic field produced about 
the conductor by the current. The best results can 
be obtained by placing the compass needle and wire 
parallel to each other when there is no current in 
the conductor. The compass needle will come to rest 
in a position which corresponds to a combination of 
the magnetic field of the earth and that produced by 
the current in the conductor. If the current in the 
conductor be increased in value, the deflection of the 
compass needle from its original value will be in¬ 
creased. The direction in which the compass needle is 
deflected will change if the direction of the current in 
the conductor is. changed. This simple experiment 
proves two things: First, the magnetic effect of the 
current depends upon the value of the current it 
increases with an increase of current and decreases 
with a decrease of current; and second, the direction 
of the magnetic field produced by the current depends 
upon the direction of the current in the conductor. 

Another method of investigating the direction of 
a magnetic field about a conductor is to place a con¬ 
ductor, in which a current may be produced, in a 
vertical position through a heavy piece of paste- 


28 


4 - 


ELECTRIC MOTORS 


board or a thin wooden board, as shown in Figure 4, 
and then determine the direction of the magnetic 
field at various points about the conductor by means 
of a small compass needle. It will be found that 
the compass needle will point in one general direction 
around the conductor for a certain direction of cur¬ 
rent and in the opposite direction when the current 
is reversed in direction. Remembering that the posi¬ 
tive direction of the magnetic field corresponds to the 
direction in which the north pole of the compass needle 
points, it will be observed that the direction of the 



Figure 4.—Direction of the Magnetic Field about a Conductor 
in which there is a Current. 

% 

magnetic field is clockwise about the conductor as you 
look in the direction of the current, and counter¬ 
clockwise as you look along the conductor in the 
opposite direction of the current. This simple rela¬ 
tion is quite useful in determining the direction of 
current in a conductor, when the direction of the 
magnetic field is known, by means of the compass 
needle. 

Another simple method of remembering the rela- 
tion of the direction of current in a conductor and 
the direction of the magnetic field due to the current, 
which is known as the right-hand rule, is as follows: 
Grasp the conductor with the right hand, the thumb 
being placed along the conductor and the fingers 




MAGNETISM, ELECTROMAGNETISM 


29 


around the conductor, then the fingers will point 
around the conductor in the direction of the ■ magnetic 
field when the thumb points in the direction of the 
current in the conductor. 

Solenoid.— The magnetic effect of an electric cur¬ 
rent may be increased by bending the conductor cai- 
rying the current into a loop. The cross-section 
through a single turn of wire carrying a current 
and the magnetic field surrounding the turn are 
shown in Figure 5. The current is away from the 



Figure 5.—-Magnetic Field about a Coil of One Turn. 

observer in the upper part of the wire and toward 
the observer in the lower part of the wire W [ 11C 
results in the direction of the magnetic field about 
the upper part being clockwise and about the lower 
part being counter-clockwise. It is apparent that the 
direction of the magnetic field due to the current m 
the different parts of the turn passes through the coil 
from the right side to the left, and each part of the 
turn acts with all the other parts on the center of 
the turn, thus making the magnetic field within the 
turn much stronger than the magnetic field outside the 
turn, which is indicated in the figure by drawing 
more lines of force per unit of area. 






so 


ELECTRIC MOTORS 


If the number of turns forming the coil be in¬ 
creased, the strength of the magnetic field inside the 
coil will be increased, since the greater part of the 
lines of force produced by each turn seem to pass 
around the entire winding instead of passing around 



Figure 6.—Magnetic Field about a Coil of Several Turns. 

the individual turns. A cross-section of a coil of 
several turns is shown in Figure 6, in which the 
majority of lines are shown passing through all the 
turns. A coil of this kind is called a solenoid. 



A solenoid, when there is a current in its winding, 
has all of the properties of a permanent magnet. 
The lines of force pass from the south pole to the 
north pole of the solenoid within the solenoid and 
from the north pole to the south pole outside the 
solenoid, just as in the case of a permanent magnet. 
The polarity of the solenoid may be determined by 
a compass needle, as shown in Figure 7, or it may 









MAGNETISM, ELECTROMAGNETISM 


31 


be determined by the following simple rule, if the 
direction of the current in the winding is known: 
Grasp the solenoid with the right hand, placing the 
fingers around it in the direction of the current, the 
thumb will then point in the direction of the north 

pole, as shown in Figure 8. 

Magnetomotive Force. —The electric current in the 
winding of a solenoid sets up a force which diivts 
the lines of magnetic force, called magnetic flux, 
through the path which they take, called the magnetic 
circuit, just as the generator in the electrical ciicuit 
produces an electromotive force which causes the elec- 


Figure 



8._How to Determine the Polarity 


of a Solenoid. 


tricity to flow in the electrical circuit. This force due 
to the current is called the magnetomotive, force, 
mm.f. (abbreviated). The value of the magnetomo¬ 
tive force varies as the product of the number of 
turns in the solenoid and the current, in amperes, t e 
turns are carrying. If we represent the number of 
turns by N and the current by I, the magnetomotiv 
force in ampere-turns will be equal to NI. A mag¬ 
netomotive force of a given value may be produced 
by any combination of current and turns such that 
their product is constant and equal to the required 
value of the magnetomotive force. For example 
ampere through 500 turns, 25 amperes through 20 
turns, 50 amperes through 10 turns, etc., will all 
produce the same magnetomotive force. 


32 


ELECTRIC MOTORS 


The unit for magnetomotive force generally used in 
magnetic calculations is the gilbert. To change from 
ampere-turns to gilberts, it is necessary to multiply 
by (47r-rl0), or 1.2566. 

Reluctance .—The magnetomotive force acting on 
any magnetic circuit encounters a certain opposition 
to the production of a magnetic flux, just as the elec¬ 
trical pressure encounters a certain opposition, called 
resistance, in the electrical circuit to the production 
of a current of electricity. The opposition offered 
by the magnetic circuit to the production of the 
magnetic flux is called its reluctance and is usually 
represented by the symbol 8. The reluctance of the 
magnetic circuit depends upon the kind of material 
composing the magnetic circuit and upon the dimen¬ 
sions of the circuit. It increases with an increase 
in length of the circuit; it decreases with an increase 
in area, all other conditions remaining constant; and 
it increases with a decrease in the value of a property 
of the material, called its permeability (which will 
be defined later) and represented by the symbol fi. 
The above relations may be written in the form of an 
equation as follows: 


reluctance = 


length of circuit in centimeters 
permeability x area in square centimeters 



/x x A. 


The unit in which reluctance is measured is called 

the oersted. 

Reluctances are added in the same manner as re¬ 
sistances. If the magnetic circuit is composed of 
several different materials, as in the case of the motor, 




MAGNETISM, ELECTROMAGNETISM 


33 


the reluctance of each part must be computed and the 
results added, which will give the reluctance of the 
entire magnetic circuit. 

Ohm’s Law for the Magnetic Circuit.— Magnetomo¬ 
tive force, reluctance, and magnetic flux are related 
to each other just as electrical pressure, resistance, 
and current are related to each other. Magnetic flux 
is measured in a unit called the maxwell; it cor¬ 
responds to one line of force and is represented by 
the symbol <f>. The relation of the quantities asso¬ 
ciated with the magnetic circuit may be given in the 
form of an equation as follows: 

. magnetomotive force 

magnetic flux =--- 

reluctance 

.. gilberts 

maxwells -- 

oersteds 

m.m.f. 


1.2566 NI 



fxA 

1.2566 NInA 

*=- 7 - 

This last equation gives the value of the magnetic 
flux a current of I amperes w T ill produce when canied 
about the magnetic circuit through N turns, the per¬ 
meability of the material composing the circuit being 
represented by ju, its area in square centimeters by 
A, and its length in centimeters by l. 








34 


ELECTRIC MOTORS 


Field Intensity, Induction Density, and Perme¬ 
ability. —The number of lines of force in a magnetic 
field in air per unit of area perpendicular to the direc¬ 
tion of the field corresponds to what is called the 
magnetic field intensity, or field strength. Field in¬ 
tensity, or field strength, is usually represented by 
the symbol H. 

If a magnetic field can be produced within a solen¬ 
oid, having no core, and a piece of magnetic material, 
such as iron, be introduced, the number of lines of 
force per unit of area will be greatly increased, al¬ 
though the current, or magnetomotive force, remains 
constant. The number of lines of force per unit area 
perpendicular to their direction in any material other 
than air corresponds to what is called flux density, 
or induction density. Induction density is usually 
represented by the symbol B. 

The ratio of the number of lines per unit of area 
in air to those in some other material, the magneto¬ 
motive force being the same in both cases, is the 
permeability. 


permeability = 


induction density 
field strength 



Magnetization Curves. —The permeability of iron 
is not constant but depends upon the degree to which 
it is magnetized. Hence, in order to compute the 
reluctance of a magnetic circuit, it is necessary to 
know either the field strength or the induction den¬ 
sity and its relation to the permeability. A magneti¬ 
zation curve is a curve showing the relation between 



MAGNETISM, ELECTROMAGNETISM 


35 


the magnetizing force and the induction density for 
a given grade of material. The relation between 
induction density and the magnetizing force is dif¬ 
ferent during the increase of magnetizing force from 
what it is during the decrease of magnetizing force. 
The tendency of the induction density to lag behind 
the magnetizing force is due to a property of the 



Figure 9.—Magnetization Curves. D —lines per s 9 ua re ineb. 

//_ampere turns per inch. No. /.—Annealed sheet steel. 

No. II .—Cast steel. No. III .—Wrought iron. 

No. IV .—Cast iron. 


material called hysteresis which is the cause of consid¬ 
erable loss in the operation of electrical machinery. 

The magnetization curves for some of the more com¬ 
mon materials are given in Figure 9. The induction 
density for the different field strengths are the aver¬ 
age of the values obtained for an increasing and a 
decreasing field strength. 

Hysteresis Loss .—When a piece of iron is magnet¬ 
ized by sending a current through a winding about 
it there is a certain amount of energy stored in the 
magnetic field. If the current in the circuit be re¬ 
duced to zero value, all of the energy used in magnet- 

































































36 


ELECTRIC MOTORS 


izing the piece of iron will not be returned to the 
circuit. This difference in the energy input and that 
returned will appear as heat, and it is called hystere¬ 
sis loss since it is supposedly due to a lag of the mag¬ 
netization behind the magnetizing force. 

A piece of iron is carried through what is called 
a magnetic cycle when its magnetism is carried from 
a maximum value in one direction through zero to a 
maximum value in the opposite direction, again 
through zero, and back to the original value. When 
a piece of iron is carried through / magnetic cycles 
per second, the loss in power in watts is given by the 
following equation: 

P h = V xK x B 1 - 6 x / x 10" 7 watts 

In the above equation V represents the volume of 
the piece in cubic centimeters, A is a constant taking 
into account the kind of iron being tested, and B is 
the maximum value of the induction density in lines 
per square centimeter. 

VALUE OF HYSTERETIC CONSTANT K FOR DIFFERENT 

MATERIALS 


Ordinary Sheet Iron.004 

Thin Sheet Iron (good).003 

Best Annealed Transformer Sheet 

Metal .0015 

Cast Steel .012 

Cast iron.016 

Forged Steel .025 


Electromagnetic Induction .—If a conductor and a 
magnetic field be moved relative to each other in 
such a manner that the conductor cuts across the 








MAGNETISM, ELECTROMAGNETISM 


37 


lines of force forming the field, there will he an 
induced electromotive force produced in the con¬ 
ductor. The direction of this induced electromotive 
force depends upon the relation between the direction 
of the magnetic field and the direction of the motion. 
If the fore finger, middle finger, and thumb of the 
right hand are placed at right angles to each other, 
and the fore finger is pointed in the direction. of 
the magnetic field and the thumb in the direction 
of the motion, then the middle finger will point in 
the direction of the induced electromotive force. 

The value of this induced electromotive force de¬ 
pends upon the rate at which the conductor is cutting 
the lines of force of the magnetic field. When the 
rate of cutting is uniform and at the rate of 100,- 
000,000 each second, there will be an induced electro¬ 
motive force of one volt in the conductor. The value 
of this induced electromotive force may be increased 
by connecting several conductors in series and moving 
them all across the magnetic field, as in the direct- 

current generator. > 

Inductance .—When a current is being established 
in a circuit, the lines of force surrounding the circuit 
and constituting the magnetic field are increasing in 
diameter. These lines of force are supposed to start 
as points at the center of the conductor and to move 
outward across the conductor as the field is increasing 
and to move inward across the conductor as the field 
is decreasing. This movement of the magnetic field 
with respect to the conductor results in there being an 
electromotive force induced in the conductor. The 
direction of this induced electromotive force will 
depend upon the direction of the relative movement 
of the magnetic field and conductor with respect to 


38 


ELECTRIC MOTORS 


each other. When the current in the conductor is 
increasing in value, the direction of the induced elec¬ 
tromotive force will be in the opposite direction to the 
current, and it tends to prevent the current increas¬ 
ing. When the current is decreasing in value, the 
direction of the induced electromotive force will be 
in the same direction as the current, and it tends to 
maintain the current, or to prevent its decreasing. 
This property of the circuit which tends to prevent 
any change in the value of the current in the circuit 
is called its self-inductance. A circuit is said to have 
one unit of self-inductance, or one henry, when there 
is an electromotive force of one volt induced in the 
circuit, due to a uniform change in the current of 
one ampere each second. 

When two electrical circuits are so related that a 
change in current in one will produce an electromotive 
force in the other, they are said to possess a mutual 
inductance. Two circuits are said to have one unit 
of mutual inductance, or one henry, with respect to 
each other when there is an electromotive force of one 
volt induced in one, due to a uniform change of 
current in the other of one ampere each second. A 
good example of the practical application of mutual 
inductance is found in the static transformer. 

Eddy Currents. —When a mass of metal is moved 
in a magnetic field, currents, called eddy currents, 
will flow through the metal. These currents will heat 
the metal and represent a loss in the operation of 
dynamo-electric machinery. 

The loss due to eddy currents is greatly reduced 
in electrical equipment by constructing the volume 
in which they occur of thin sheets of metal, called 
laminations, arranged in such a way that their planes 


MAGNETISM, ELECTROMAGNETISM 


39 


are perpendicular to the direction in which the eddy 
currents tend to flow. A good example of such con¬ 
struction is found in transformer and armature cores. 

The eddy-current loss occurring in a given volume 
of iron may be calculated by means of the following 
equation: 

P e = Vxf 2 xt 2 xB 2 xK 

in which V is the volume of the iron in cubic centime¬ 
ters ; / is the frequency of the magnetic cycles per 
second; t is the thickness of the laminations in cen¬ 
timeters ; B is the maximum induction density in lines 
per square centimeter; and A is a constant, depend¬ 
ing upon the resistance of the iron per cubic centime¬ 
ter, which is usually about 1.6x10 n . 


CHAPTER III 


ALTERNATING-CURRENT ELECTRICAL CIRCUITS 

Definition of Alternating Electromotive Force , or 
Current .—An alternating electromotive force, or cur¬ 
rent, is one that reverses in direction at certain regu¬ 
lar intervals and at the same time it may be con¬ 
tinuously changing in value. Such an electromotive 
force would be induced in a loop of wire if it were 
revolved in a magnetic field as shown in Figure 10. 



Figure 10.—Single Loop Revolving in a Magnetic Field. 

This alternating electromotive force will produce an 
alternating current in the loop of wire if the ends 
be connected, or a current may be produced in an 
external circuit if the terminals of the loop be con¬ 
nected to the circuit by means of slip rings and 
brushes as shown in the figure. These slip rings are 
nothing more than two metal rings insulated from 
each other and connected to the terminals of the coil, 
one to each end. Two brushes bear upon the rings 
and thus provide a continuous connection between the 
coil and the external circuit. 


40 












ALTERNATING-CURRENT ELECTRICAL CIRCUITS 41 

The value of the electromotive force induced in the 
coil at any instant will depend upon the rapidity with 
which the sides of the coil are cutting across the lines 
of force of the magnetic field. It can be readily seen 
from an inspection of the figure that the sides of the 
coil are moving perpendicular to the direction of the 
magnetic field when the coil is in a horizontal position 
and, as a result, they are cutting the lines of force 
at the greatest rate. When the coil is in a vertical 
position, the sides are moving parallel to the direc¬ 
tion of the magnetic field and they are cutting no 
lines of force. For intermediate positions the rate 



Figure 11 .—Electromotive Force Induced in a Single Loop. 


at which the lines will be cut will depend upon the 
sine of the angle between the position of the coil and 
a plane perpendicular to the direction of the magnetic 











42 


ELECTRIC MOTORS 


will increase in value for the first 90 degrees, when 
it reaches its maximum value. It then decreases in 
value for the next 90 degrees and is zero at the end 
of 180 degrees, or one-half revolution. The values 
of the electromotive force are repeated for the re¬ 
maining half revolution but in the opposite direction, 
since the motion of the sides of the coil with respect to 
the field is reversed. This is represented in the figure 
by drawing one-half. of the curve below and one- 
half above the horizontal line. 

Cycle, Frequency, Alternation, Period, Synchro¬ 
nism, and Phase Displacement. —When an alternating 
electromotive force, or current, has passed through a 
complete set of positive and negative values, starting 
at any value and again returning to that value in the 
same direction, it has completed what is called a 
cycle. A complete set of positive and negative values, 
or one cycle, is shown by the curve in Figure 11. 

The number of cycles the electromotive force, or 
current, passes through in one second is called the 
frequency. Thus, a 60-cycle electromotive force, or 
current, would be one that passed through a com¬ 
plete set of positive and negative values 60 times 
per second. 

An alternation is one-half of a cycle and cor¬ 
responds to a complete set of positive or negative 
values of electromotive force, or current. The num¬ 
ber of alternations in a given time is equal to twice 
the frequency, or a frequency of 60 cycles would 
mean 120 alternations per second. 

The period of an electromotive force, or current, is 
the time in seconds required to complete one cycle. 
Thus the period of a 60-cycle electromotive force 
would be one-sixtieth of a second. 


ALTERNATING-CURRENT ELECTRICAL CIRCLITS 43 

Two electromotive forces, or currents, are said to 
be in synchronism when they have the same frequency. 

Electromotive forces and currents are said to be 
in phase when they pass through corresponding values 
of their respective cycles at the same time. The two 
curves shown in Figure 12 do not pass through zero 
or their maximum points at the same time and, t leie- 
fore they are said to be displaced in phase. 

Let us assume that curve E, Figure 12, represents 
the electromotive force acting on a circuit, and that 
curve I represents the current produced by this elec- 


Figure 12.—Two Curves 


Displaced in Phase. 



tromotive force. It will be seen by a careful inspec¬ 
tion of the figure that curve I passes through zero 
value in the positive direction after the .electromo¬ 
tive force curve E, or the current is lagging behind 
the electromotive force. 

The phase displacement of two quantities with re- 
spect to each other is usually measured in degrees. 
The total length of the line AC, Figure' ’ 

sponds to 360 degrees, or one cycle of the d* 
motive • and likewise the length of the line D G, h 
is equal in length to AC, corresponds to.one cycle 
of current. The two curves are displaced in P 
from each other the same fractional part of 360 de- 
«. the length .( the line -4 » » * P>« ^ 

This displacement may be measured in time as 









44 


ELECTRIC MOTORS 


as in degrees, but it is equal to such a fractional 
part of the period as the length of the line AD is a 
part of the line A C. 

Maximum, Average, and Effective Values of Elec - 
tromotive Force and Current .—The maximum value 
of an alternating electromotive force, or current, is 
the value of the electromotive force, or current, rep¬ 
resented by the maximum ordinate of the electromo¬ 
tive force, or current, curve. 

The average value of an alternating electromotive 
force, or current, is equal to the average of all of 



Figure 13.—Relation of Maximum and Average Values. 


the instantaneous electromotive forces, or currents, 
for a complete alternation. The average value of a 
sine-wave electromotive force, or current, is equal to 
.636 of the maximum value, as shown in Figure 13. 

The effective value of an alternating current is 
numerically equal to a steady direct current that will 
produce the same heating effect in a given time as is 
produced by the alternating current in a like time. 
Since the heating effect of a current varies as the 
square of the current, then the average heating effect 
of an alternating current will be proportional to the 
average value of the instantaneous currents squared ; 
and the effective current will be equal to the square 
root of the average value of the instantaneous currents 
squared. The effective value of a sine-wave alter- 















ALTERNATING-CURRENT electrical CIRCUITS 45 

nating current is equal to .707 of the maximum value, 
as shown in Figure 14. 

The effective value of an alternating electromotive 
force bears the same relation to its maximum value as 
exists between the effective and the maximum values 
of the currents, namely, the effective electromotive 
force is equal to ./0/ times the maximum. 

Alternating-current ammeters and voltmeters indi¬ 
cate the effective values of current and electrical 

pressure. 

The form factor of a wave representing the value 
of a current or electromotive force is numerically equal 



Figure 14.—Relation of Maximum and Effective Values. 

to the effective value divided by the average value. 
For a sine wave it is 1.11. In the following calcula¬ 
tions the current and electromotive force are assumed 
to follow a sine curve. 

Ohm’s Law for the Alter nating-Current Circuit. 
When an alternating electrical pressure acts upon a 
closed circuit, the effective current produced is equal 
to the effective pressure divided by the resistance 
of the circuit, provided there is no capacity or induc¬ 
tance in the circuit. If capacity or inductance or 
both, be present in the circuit, the total, opposition 
offered by the circuit to the flow of electric,ty through 
it will be greater than the ohmic resistance of the 
circuit unless the effects of capacity and inductance 

















46 


ELECTRIC MOTORS 


neutralize each other, as will be explained later, in 
which case the opposition offered is equal to the 
ohmic resistance of the circuit. The combined effects 
of resistance, inductance, and capacity in opposing 
the free flow of electricity through a circuit is called 
the impedance of the circuit. The combined effects 
of the capacity and inductance is called the reactance 
of the circuit; the effect of capacity is called capacity 
reactance; and the effect of inductance is called in¬ 
ductive reactance. Reactance and impedance are 
both measured in ohms. The symbol generally used 
for impedance is Z, and that for reactance X , it being 
given a subscript C when it represents capacity react¬ 
ance and a subscript L when it represents inductive 
reactance. 

Ohm’s law for the alternating-current circuit may 
be written as follows: 


effective current = 


effective pressure 
impedance 


volts 

amperes =- 

ohms 


1 


E_ 

Z 


Effect of Inductance in an Alternating-Current 
Circuit .—The action of inductance in an alternating- 
current circuit is to cause the current to lag the 
electrical pressure, and, if the circuit contains induc¬ 
tance alone, the current and the electrical pressure 
will be displaced in phase from each other by 90 
degrees. 

The pressure required to produce a current of 1 




ALTERNATING-CURRENT ELECTRICAL CIRCUITS 47 

amperes in an inductance of L henries is given by tbe 
following equation: 

£ l = 6.2832x/xLx7 

in which / represents the frequency of the current in 
cycles per second. 

* The inductive reactance X L is given by the follow¬ 
ing equation: 

X L = 6.2832 x/xL ohms 

Effect of Capacity in an Alternating-Current Cir¬ 
cuit. _Two electrical conductors which are separated 

by some insulator, such as air, rubber, glass, mica, 
etc., constitute what is called a condenser. The me¬ 
dium separating the two conductors is called the 
dielectric . The action of a condenser m an electrical 
circuit is very similar to the action of an elastic 
diaphragm, such as rubber, stretched across a pipe 
upon which there is an alternating pressure acting. 
The action of capacity in an alternating-current cir¬ 
cuit is to cause the current to lead the electnca 
pressure, and, if the circuit contains capacity alone, 
the current and the electrical pressure will be dis¬ 
placed in phase by 90 degrees. 

The pressure required to produce a curren 
amperes in a capacity of C farads is given by the 

following equation: 

Ec= 6.2832 x/xC" 

The capacity reactance X c is given by the following 
equation: 

Xc= 6.2832 x/xC 





48 


ELECTRIC MOTORS 


Combined Effects of Resistance, Inductance, and 
Capacity in an Alternating-Current Circuit .—The re¬ 
sistance of an alternating-current circuit simply op¬ 
poses the free flow of electricity through it without 
producing any phase displacement of the current and 
the electrical pressure. 

The current required to produce a pressure of I 
amperes through a resistance of R ohms is given by 
the following equation: 

E r = RxI 



The three pressures E R , E R , and E c may be repre¬ 
sented as shown in the diagram in Figure 15. Since 
E c and E h are exactly opposite, one may be subtracted 
from the other as indicated in the figure in order to 
determine the resultant. This resultant is at right 
angles to E R and it must be combined with E R in 
order to get the value of E which is the resultant of 
all three pressures. 

E = \/£ r 2 +(£ l -£c ) 2 


or 


E = yj{El) 2 + ^6.2832 xfxLxI-- 


2832 x/xC 











alternating-current electrical circuits 49 

By taking I from under the radical sign, this equa¬ 
tion may be written as follows: 


or 

E 

l- "T C 

^ + ( 6 .2332x/xL- 62832x/ -) 

The above equation gives the value of the effective 
current I, in amperes, in terms of the impressed 
effective electrical pressure E, in volts; of the resist¬ 
ance B, in ohms; of the inductance L, in henries; ol 
the capacity C, in farads; and of the frequency /, 

in cycles per second. T 

Series Alternating-Current Circuit .—In a series 
alternating-current circuit, the current is the same m 
all parts of the circuit just as in the series direct- 
current circuit. The sum of the electrical pressures 
over the various parts of a series circuit is not neces¬ 
sarily equal to the total pressure acting on the cir¬ 
cuit when it is carrying an alternating current, unless 
the phase relation of the current in the circuit and 
the pressure over .the various parts are the same, n 
general, the total pressure acting on the series, circuit, 
when it is carrying an alternating current, is equal 
to the vector sum of the pressures over the different 

series circuit composed of a resistance B, an 
inductance L, and a capacity C, is shown diagram- 














50 


ELECTRIC MOTORS 


matically in Figure 16. The total pressure may be 
determined as indicated in Figure 15. 

Divided Alternating-Current Circuit. —The sum of 
the currents in the several branches of a divided cir¬ 
cuit is equal to the total current, when the circuit is 
carrying a direct current. If the circuit is carrying 
an alternating current, the sum of the currents in the 
different branches will not be equal to the total cur¬ 
rent unless the phase relation of the current in the 
different branches and the electrical pressure acting 
on the divided portion are the same for each branch. 



In general, the total current in a divided circuit is 
equal to the vector sum of the various branch cur¬ 
rents. The vector sum of the two currents is deter¬ 
mined in the same manner as the resultant of two 
forces would be determined. If the two forces are 
in the same direction, the resultant is equal to their 
sum; if they are in opposite directions, the resultant 
is equal to their difference; if they are at right angles 
to each other, the resultant is equal to the square root 
of the sum of the squares of the two forces, etc. 

Instantaneous Power in an Alternating-Current 
Circuit .—The instantaneous power in an alternating- 
current circuit at any instant is equal to the product 
of the current in the circuit at that instant and the 























alternating-current electrical circuits 51 

electrical pressure acting on the circuit at that in¬ 
stant. The two curves E and I, Figure IT, represent 
the pressure acting on a circuit and the current in 
the circuit, both being drawn to a suitable scale. 
A third curve may be drawn having ordinates propor- 



Figure 17 . — Instantaneous Power. Current and Pleasure 


tional to the product of the quantities represented 
by the curves E and 1, as indicated by l, m the 

fi8 If' tfie current and the electrical pressure be dis¬ 
placed in phase, as shown in Figure 18, the ordinates. 



of the CUrVe r S e i n tL Cl product oTthf q^anXs- 

represented by these'ordinates is not positive^ 
out the cycle, but is negative m sign for a port on 
of the time, which results in a portion of the cu 
P being below the horizontal line. 
























52 


ELECTRIC MOTORS 


When the current and the pressure are in phase, 
or there is no resultant reactance, the power is all 
positive; that is, no power is being returned from the 
circuit to the generator. The power in such a case is 
proportional to the combined area of the loops in the 
power curve. 

If the current and the pressure are not in phase, 
or the resultant reactance in the circuit is not zero, 
the effective power is proportional to the difference 
in the areas of the positive and the negative loops 
of the power curve, because the negative loops of 
the power curve represent power which is being 
returned from the line to the generator. 

True Power in Alternating-Current Circuit .—The 
true power in an alternating-current circuit, in watts, 
in which the current and the pressure are in phase, 
is equal to the product of the effective values of the 
current and the pressure. The true power in an 
alternating-current circuit in which the current and 
the electrical pressure are displaced in phase by 90 
degrees is zero, because the area of the positive and 
the negative loops of the power curve are the same 
and just as much power is returned to the generator 
as the generator delivers to the circuit. This condi¬ 
tion is impossible in practice, as all circuits contain 
some resistance and, as a result, the current and 
the pressure can never be displaced in phase by 90 
degrees. 

The current and pressure are usually displaced in 
phase from each other, and the amount of this dis¬ 
placement depends upon the relation between the 
resultant reactance and the resistance of the circuit. 
The current, for convenience, may be thought of as 
composed of two parts: one in phase with the elec- 


ALTERNATING-CURRENT ELECTRICAL CIRCUITS 53 

trical pressure, and the other at right angles to the 
electrical pressures. From the previous discussion, 
it is obvious that there is no resultant power due to 
the part of the current at right angles to the pres¬ 
sure, as the positive and the negative power loops 
are equal in area. The power due to the part of the 
current in phase with the pressure is all positive, or, 
if it was the only current in the circuit, the generator 
would be delivering power all the time. In order to 
calculate the true power in an alternating-current 
circuit, it is necessary to determine the value of the 
part of the current in phase with the pressure, and 
then multiply the effective value of this part of the 
current by the effective pressure. 

The part of the current in phase with the pressure 
is equal to the total current I multiplied by the cosine 
of the angle between the current and the pressure. 
The true power, then, is equal to 

P = E x I xcos# 

The product of E and 1 in the above equation is 
called the apparent power; and the quantity cos 0 
is called the power factor, because it is the factor by 
which the apparent power must be multiplied in order 
to obtain the true or effective power. If the current 
and the pressure are in phase, the angle between them 
is zero and the cosine of 6 is equal to unity, which 

results in 

P = ExIxl = ExI 

Single-, Two-, and Three-Phase Circuits.—A single 
loop of wire revolving in a magnetic field, as shown 
in Figure 10, corresponds to what is called a single- 
phase alternating-current generator. 


64 


ELECTRIC MOTORS 


If a second loop of wire be mounted on the shaft 
with the first in such a position that the planes of 
the coils are at right angles to each other, the electro¬ 
motive forces in the two loops will be displaced in 
phase by 90 degrees, and the combination corresponds 
to what is called a two-phase circuit. Each loop may 
be provided with two slip rings and be connected to 
independent circuits, or one ring may be common to 
both loops, in which case only three rings and three 
brushes are required, as shown in Figures 19 and 20. 



Figure 19.—Four-Ring Two-Phase Alternator. Figure 20.— 
Three-Ring Two-Phase Alternator. Figure 21.— 
Six-Ring Three-Phase Alternator. 


If three loops of wire, whose planes are 60 degrees 
apart, be revolved in a magnetic field, there will be 
electromotive forces induced in the loops which will 
be displaced in phase from each other by 120 degrees. 
Each of these loops may be provided with two slip 
rings and two brushes and such be connected to 
independent circuits, as shown in Figure 21, or three 
loops may be interconnected and only three rings 
and three brushes will be needed. Two possible meth¬ 
ods of connecting the three loops are shown in Figures 
22 and 23. The loops are said to be delta-connected 
in Figure 22, and star-connected in Figure 23. The 
delta connection is usually represented by the symbol 
A, and the star connection by the letter Y. 
















































ALTERNATING-CURRENT ELECTRICAL CIRCUITS 55 


The following relations hold for the voltage and 
the current relations for the two connections, when 
the loads are balanced. The voltage between lines 
in the delta connection is equal to the voltage in each 



Fig. 22. 



Figure 


22.—Delta-Connected 
—Star-Connected 


Three-Phase Alternator. 
Three-Phase Alternator. 


Figure 23. 


loop, and the current in each outside line is equal to 
the V 3 times the current in each loop. . In the star 
connection, the current in the different lines is equa 
to the current in the loop connected to that line, 

and the voltage between lines is equal to the V 3 times 
the voltage in each loop. 




























CHAPTER IY 


ELECTRICAL MEASUREMENTS 

Measurement of Current .—The current in a circuit 
is measured by means of an instrument called an am¬ 
meter. The operation of the ammeter depends upon 
some effect of the current, such as the heating effect, 
magnetic effect, etc., and, since the magnitude of 
these various effects vary with the value of the cur¬ 
rent, it is possible to determine the value of the 



Figure 24.—Froper Connection of Ammeter and Voltmeter. 


current by determining the magnitude of the effect. 
The scales of the ammeters, however, are usually 
marked to read directly in amperes, or current, in¬ 
stead of indicating the value of the effect of the 
current. 

Ammeters are always connected directly in series 
with the circuit in which it is desired to measure the 
current, as indicated in Figure 24, which shows an 
ammeter A connected directly in one of the lines lead- 

56 





















ELECTRICAL MEASUREMENTS 


57 


ing to the motor M. This ammeter will indicate the 
total current supplied to the motor. 

The resistance of an ammeter should be very small 
in order that the power required to operate it be 

small. 

An ammeter shunt is a resistance of low value 
which may be connected in parallel with an ammeter 
and thus increase the value of the current that it is 
possible to measure with the ammeter. When the 
resistance of the shunt bears a definite relation to the 
resistance of the ammeter, there will be a definite part 
of the total current in the ammeter circuit. For 
example, if the resistance of the ammeter circuit is 
four times the resistance of the shunt circuit, only 
one-fifth of the total current will pass through the 
ammeter and the value of this current as indicated 
by the ammeter must be multiplied by five m order to 
get the value of the total current. An ammeter shunt 
can be used in measuring direct current only, since 
the relation of the currents in the two branches of a 
divided circuit, when it is carrying alternating cur¬ 
rent, is not necessarily equal to the inverse relation 
between the resistances of the two branches. . 

When it is desired to measure an alternating cur¬ 
rent in excess of the current capacity of the am¬ 
meter use is made of a device called a current trans¬ 
former. The construction of the current transformer 
is such that the current in the secondary winding is 
a definite part of the current in the primary winding. 
A low-reading ammeter may be used to measure the 
current in the secondary winding, and this current 
multiplied by the ratio of primary to secondary cur¬ 
rents will give the value of the current in the primary 
circuit or line, since the primary part of the trans- 


58 


ELECTRIC MOTORS 


former is in series with the line in which it is desired 
to measure the current. A switchboard type of cur¬ 
rent transformer is shown in Figure 25. 

Measurement of Pressure .—The difference in elec¬ 
trical pressure between any two points on an electrical 
circuit may be determined by means of an instrument 
called a voltmeter. Voltmeters operate on the same 
general principles as ammeters; that is, their indica¬ 
tion depends upon the value of the current passing 
through them. The value of the current in the volt- 



Figure 25.—Switchboard Type of Current Transformer. 

meter will depend upon the resistance of the voltmeter 
and the pressure to which it is connected and this 
current will vary directly as the pressure, if the 
resistance remains constant, which results in the volt¬ 
meter indication varying with the difference in pres¬ 
sure between its terminals. The proper method of 
connecting a voltmeter is shown in Figure 24. It is 
desirable to have the resistance of voltmeters as large 
as possible. 

The capacity of a direct-current voltmeter and of 
some alternating-current voltmeters may be increased 
by connecting a resistance, called a multiplier, in 
series with the voltmeter. For example, if a volt¬ 
meter has a resistance of 15 000 ohms and a resist- 














ELECTRICAL, MEASUREMENTS 


59 


ance of 60,000 ohms is connected in series with it, 
then the total pressure acting on the two in series 
will be equal to the voltmeter indication multiplied 
by five, since only one-fifth of the total pressure will 
be between the terminals of the voltmeter as its re¬ 
sistance is one-fifth of the total resistance. 

A low-reading alternating-current voltmeter may 
be used in measuring high electrical pressures by 
means of a device called a potential transformer. The 
voltage between the terminals of the secondary wind¬ 
ing may be measured by means of the voltmeter, and 


Figure 26.—Potential Transformer. 

this reading multiplied by the ratio between the 
primary and the secondary voltages will give the value 
of the voltage between the terminals of the primary 
winding. A pressure, or potential, transformer is 
shown in Figure 26. When a potential transformer 
is used, the indicating instrument is .entirely insulated 
from the high pressure, and there is very little like¬ 
lihood of the instrument being injured or of the at¬ 
tendants getting in contact with the high-pressure 

circuit. . _ . , 

Drop in Potential Method of Measuring Resistance. 

—The value of a resistance may be determined by 

sending a current through it and measuring the dif- 

ference in pressure between the termina s o 





60 


ELECTRIC MOTORS 


resistance for a definite value of current. The scheme 
of connection is shown cliagrammatically in Figure 
27, in which R represents the resistance to be meas¬ 
ured ; A is an ammeter connected in series with the 
resistance ; R is a battery to be used in sending a 
current through the resistance—any source of direct 
current may be used; Rh is a rheostat which may be 
used to control the value of the current; and V is a 
voltmeter for measuring the difference in pressure 
between the terminals of the resistance. If the cur- 



Figure 27.—Drop in Potential Method of Measuring Resistance. 


rent through the voltmeter be neglected, then the 
ammeter will indicate the current through the resist¬ 
ance R, and the value of the resistance R is equal to 
the pressure in volts, as indicated by the voltmeter, 
divided by the current in amperes, as indicated by the 
ammeter A , or 



When the resistance of the voltmeter circuit is large 
in comparison to the value of the resistance R, the 
current through the voltmeter is small in comparison 
to the current through the resistance R and may be 
neglected. In some cases the current through the volt- 
























electrical measurements 


61 


meter cannot be neglected but must be subtracted 
from the value of the current as indicated by the 
ammeter in order to obtain the value of the current 
in the resistance being measured. The current in 
the voltmeter is equal to the value of the pressure as 
indicated by the voltmeter divided by the resistance 
of the voltmeter Ry, or 



The current Zr through the resistance R, then, is 


or 


Zr = Z-Z v 



and the value of the unknown resistance will be 



”- x R v 

IR V -E 

This method of measuring resistance may be used 
in measuring the resistance of armatures, fields, etc. 
Series-Voltmeter Method of Measuring Resistance. 

_The scheme of connections for measuring resistance 

by the series-voltmeter method is shown in Figure 28. 
A voltmeter V is connected in series with an electrical 
pressure produced by the direct-current generator G 
and the unknown resistance, which in this case is the 
resistance between an insulated wire and the metal 



62 


ELECTRIC MOTORS 


pipe, the circuit being completed through the ground. 
The electrical pressure produced by the generator will 
be distributed around the above circuit in propor¬ 
tion to the resistance of the different parts. The 
pressure between the voltmeter terminals, which will 
be indicated by the voltmeter, will bear the same 
relation to the pressure over the unknown resistance 
as the resistance of the voltmeter bears to the value 
of the unknown resistance. The pressure over the 
unknown resistance will be equal to the total pres- 



Figure 28.—Series-Voltmeter Method of Measuring Resistance. 


sure produced by the generator minus the pressure 
over the voltmeter. The total pressure may be deter¬ 
mined by connecting the voltmeter directly across 
the terminals of the machine, or, if the pressure is 
rather unsteady, it may be best to use a second volt¬ 
meter V Q . Representing the total pressure by E , 
the pressure between the terminals of the voltmeter 
by Ey, and the pressure over the unknown resistance 
by E x , we have the following equation: 

E X = E -Ey 

0 

The current in the voltmeter and the unknown resist¬ 
ance will be the same and are equal to the pressure 














63 


ELECTRICAL MEASUREMENTS 


E v indicated by the voltmeter divided by the resist- 
ance of the voltmeter Ry, or 



Ry 


Now the value of the unknown resistance K x is equal 
to the pressure between its terminals divided by the 
current it is carrying, or 



Ex. 

I 


Ey 

Measurement of Resistance by Wheatstone Bridge , 

_The connections of the various elements of a simple 

Wheatstone bridge are shown diagrammatically in 



Figure 29. The resistances A and B are called the 
ratio arms , and they are usually composed of a num¬ 
ber of resistances differing in value by multiples ot 
10, the lowest being perhaps .1 ohm and the largest 
10,000 ohms. The resistance R is called the r^n.ynt 
jf’the bridge; it is usually composed of a 









64 


ELECTRIC MOTORS 


ber of resistances ranging in value from .1 ohm tx 
several thousand ohms. In commercial types ot 
Wheatstone bridges, the various parts of these re 
sistances may be connected in circuit, or not, bj 
means of suitable switching devices. The resistance 
X corresponds to the unknown resistance whose value 
is to be determined. A galvanometer G and a battery 
are connected as indicated with keys K 2 and K x in 
circuit. When a balance of the bridge is obtained— 
that is, when there is no current through the gal. 
vanometer with both keys K x and K 2 closed, the ratio 
of the resistance X to the resistance R will be the 
same as the ratio of the resistance B to the resistance 

A, or 

X = B_ 

R~ A 

and 

X=-R 

A 

If the resistances A and B are equal when a balance 
is obtained, then the resistances R and X will be 
equal. If the resistance A is ten times the resistance 

B , then the resistance R will be ten times the resist¬ 
ance X, or vice versa. 

Commercial Wheatstone bridges assume a number 
of different forms, but they all operate on the same 
fundamental principle. 

Voltmeter-Ammeter Method of Measuring Power .— 
The power in watts in a direct-current circuit is 
equal to the product of the current in amperes and 
the pressure in volts. In an alternating-current cir. 
cuit, the product of the current in amperes and the 
pressure in volts gives the power only when the cur 


ELECTRICAL MEASUREMENTS 


65 


rent and the pressure are in phase. When they are 
not in phase, their product must be multiplied by a 
factor, called the power factor, in order to obtain 
the value of the true power. 

The power taken by a motor may be measured by 
means of a voltmeter and an ammeter, as shown in 
Figure 24. In this case the ammeter A indicates the 
comsPhned currents through the motor and voltmeter, 
but the voltmeter current is usually so small in com¬ 
parison to the total current that it may be neglected 
without causing an appreciable error. This method 
cannot be relied upon for an alternating current, as 
the current and the pressure are out of phase in the 
majority of cases, and an instrument called a watt¬ 
meter must be used. 

Indicating Wattmeter .—A wattmeter is an instru¬ 
ment for measuring pow T er, and its indication depends 
upon the combined effects of the load current, or a 
definite part of it, in the circuit in which the power 
is being measured and of the pressure acting on the 
load. If the current and the pressure are in phase, the 
force acting on the moving system will remain constant 
in direction; while, if they are displaced in phase, 
the force acting on the moving system will reverse 
in direction, and the resultant deflection will be 
produced by an average force which will be propor¬ 
tional to the difference in the forces acting in the two 
directions. Such an instrument will indicate the true 
power regardless of the phase relation of the current 
and the pressure. 

Power in a Two-Phase Circuit .—The total power in 
a two-phase four-wire or three-wire system is equal 
to the sum of the power in the separate phases. The 
power in each phase may be determined by connect- 


<56 


ELECTRIC MOTORS 


ing the series coil of the wattmeter in circuit so as to 
measure the current in that phase and its pressure 
coil across the pressure of that phase. 

A single wattmeter may be used in measuring the 
power in a three-wire two-phase system, balanced or 
unbalanced load, by connecting the series coil in the 
neutral or common wire and then take two readings: 
first, with the pressure coil connected between the 
neutral and one outside wire; and second, between the 
neutral and the other outside wire. If the connection 
of the pressure circuit to the common wire must be 
changed in order that the wattmeter read in the same 
direction in both cases, the difference of the two watt¬ 
meter readings represents the total power; while, if 
the two wattmeters read in the same direction with¬ 
out any change in the connection of the pressure 
circuit to the common wire, the sum of the two read¬ 
ings represents the total power. 

Power in a Three-Phase Circuit .—The total power 
in a balanced three-phase three-wire system is equal 
to the product of the current in one of the lines, the 
pressure between lines, and the V3, or 

P=\/3EI watts 

The power in a balanced three-phase three-wire or 
four-wire system may be measured by a single watt¬ 
meter by connecting the series coil of the wattmeter 
in one of the main lines and the pressure coil across 
the pressure of the phase in which the current coil 
is connected. This wattmeter reading multiplied by 
three will give the total power. In a four-wire sys¬ 
tem, the pressure of any phase exists between the line 
of that phase and the neutral. In a three-wire sys- 


ELECTRICAL MEASUREMENTS 


67 


tem, an artificial neutral will have to be established, 
which may be done by means of a Y box. 

The total power in a three-phase three-wire or four- 
wire system may be measured by means of two watt¬ 
meters as follows: The series coils of the wattmeters 
are connected in two of the lines and the pressure 
coil of each of the wattmeters is connected between 
the line in which its series coil is connected and the 
line in which there is no series coil. If the power 
factor of the system is greater than one-half, the 
sum of the two wattmeter readings gives the total 
power; while, if the power factor is less than one- 
half, the difference of the two readings gives the 
total power. If the readings of both wattmeters in¬ 
crease in value as the load is increased, the power 
factor is greater than one-half, and, if the reading of 
one wattmeter increases and the other decreases as 
the load increases, the power factor is less than one- 

half. 

Using Electrical Instruments .—Permanent connec¬ 
tions should not be made until the operator is sure 
that the capacity of a meter will not be exceeded by 
the voltage or amperage. Cables attached to meters 
should not be altered as they form part of the instru¬ 
ment's resistance. If the meter is found to be slug¬ 
gish, readings may be taken while tapping the case 
with the finger. Meters of any type generally give 
the best results when laid flat when in use, although 
portable types may be used in any position. Switch¬ 
board instruments are, of course, designed for a ver¬ 
tical position. Care is required if meters are to retain 
their accuracy. 


CHAPTER V 


ARMATURE WINDING FOR DIRECT-CURRENT MOTORS 

Types of Armature Cores .—Armatures may be di¬ 
vided into three general classes, according to the 
shape of the cores and the manner in which the wind¬ 
ing is placed upon the core. These classes are: 

(a) Ring armatures 

(b) Drum armatures 

(c) Disk armatures 

(a) The ring armature is one in which the core is 
in the shape of a ring, and the winding passes in *nd 



t + 


Figure 30.—Ring Armature. 

out around the core as shown in Figure 30. Th* por¬ 
tion of the winding inside the ring cuts no lines of 
force and, as a result, does not help in producing the 
required electrical pressure, in the case of the gen¬ 
erator, or the torque, in the case of the motor. 














































ARMATURE WINDING 


60 


(b) In the drum armature, the amount of wire 
which is effective in producing the electrical pressure 
in the generator and the torque in the motor is a 
larger part of the total amount, since the wire is 
wound back and forth across the surface of the core, 
which is in the form of a drum. 

(c) In the disk armature, the portion of the wind¬ 
ing in which the electrical pressure is generated in¬ 
stead of being on the cylindrical surface, as in the 
case of the ring and drum types, is on the flat sides 
of a disk, and the poles are also placed on opposite 
sides of this disk instead of being placed around 
its outer edge. The drum armature is used almost 
entirely, as it does not require hand winding, and 
the coils can be wound and formed independent of 
the armature. 

Types of Windings .—All of the armature windings 
for both direct- and alternating-current machines be¬ 
long to one of two classes: 

(a) Open-coil windings 

(b) Closed-coil windings 

(a) The open-coil winding is one in which, start¬ 
ing at one terminal of the winding and tracing 
through the winding, a “dead-end” is finally reached. 
Open-coil windings are at present used entirely on 

alternating-current machines. 

(b) The closed-coil winding is one in which, start¬ 
ing at any point on the winding and tracing through 
the winding, the starting point will be reached after 
having passed through all, or some sub-multiple of, 
the conductors forming the winding. 

Winding Element .—The element of an armature 
winding may be defined as that portion of a winding, 


70 


ELECTRIC MOTORS 


which, beginning at a commutator segment, ends at 
the next commutator segment encountered in tracing 
through the winding. 

An element may consist of more than one turn, 
as shown in Figure 31, which represents three ele¬ 
ments for different types of armature windings, and 
each element is composed of two turns. The number 
of turns in each element should be as small as pos¬ 
sible, in order that its self-inductance be small, which 
results in better commutation than could occur if 
the elements had a high self-inductance. 



Figure 31.—Elements of an Armature Winding, (a.) Ring 
Winding, (b.) Lap Winding., (c.) Wave Winding. 


The part of the winding in which the electromotive 
force is induced is called a conductor , and the num¬ 
ber of conductors in any winding will be equal to the 
number of times the winding passes from one end 
to the other under the poles. In a ring winding, 
there is only one conductor per turn; while in the 
drum winding there are two conductors per turn. 

Lap and Wave Windings .—The meaning of the 
terms lap and wave as used in defining a certain 
type of winding will be evident from an inspection 
of Figures 32 and 33. In Figure 32, the various ele¬ 
ments lap back on each other, while in Figure 33 they 
■ progress continuously in a wave-fashion around the 
armature. Lap and wave windings are often called 
parallel and series windings, respectively. 
















ARMATURE WINDING 


71 


Front and Back Winding Pitch, and Commutator 
Pitch .—In speaking of an armature, the commutator 
end is called the front of the armature and the other 
end is called the back of the armature. If all of the 



Figure 33.—Simplex Singly Re-entrant Wave Winding. 


conductors forming the armature winding be num¬ 
bered in regular order all the way around the arma¬ 
ture, then the back pitch of the winding will be 
numerically equal to the difference in the numbers 
of the conductors connected together at the back 
















72 


ELECTRIC MOTORS 


end of the armature. Likewise the front pitch will 
be equal to the difference in the numbers of the con¬ 
ductors connected together at the front end of the 
armature. In the lap winding, the front and back 
pitches are of opposite sign, because in tracing 
through the winding you pass around the armature 
core in opposite directions at the two ends. In the 
wave winding, the front and back pitches are of the 
same sign, because in tracing through the winding 
you pass around the armature core in the same direc¬ 
tion at the two ends. 

If the commutator segments be numbered consecu¬ 
tively around the commutator, then the commutator 
pitch will be equal to the difference in the numbers 
of the commutator segments connected directly to the 
terminals of any element. 

Simplex and Multiplex Windings; Degree of Re- 
entrancy .—If all of the conductors forming the arma¬ 
ture winding be interconnected as shown in Figures 
32, 33, 34, 35, 36, and 37, the winding is said to be 
singly re-entrant, because it closes on itself only 
once. If it were possible to remove a singly re-entrant 
armature winding from the armature core without 
disturbing any of the various electrical connections, 
there would be one large loop of wire formed with 
the commutator segments connected at regular in¬ 
tervals. 

Figures 32 and 34 are two different methods of 
representing a lap winding, and Figures 33 and 35 
are two different methods of representing a wave 
winding. 

It will be observed that in tracing through an ele¬ 
ment of the winding shown in Figure 34 that the 
terminals of an element are connected to commutator 


ARMATURE WINDING 


73 


segments which are adjacent to each other, while in 
Figure 36 the terminals of an element are connected 
to commutator segments which are two removed from 
each other. A lap winding whose elements terminate 
at adjacent commutator segments is called a simplex 



Figure 34.—Simplex Singly Re-entrant Lap Winding. 



Figure 35.—Simplex Singly Re-entrant Wave Winding. 


winding; one whose elements terminate at commu¬ 
tator segments separated by one segment is called a 
duplex winding; if the commutator segments are sep¬ 
arated by two segments, it is called a triplex wind¬ 
ing, etc. 

You will observe that after you have traced 
through two elements of the winding shown in Fig¬ 
ure 35, you arrive at a commutator segment one re- 





























































































74 


ELECTRIC MOTORS 


moved from the one from which you started; while 
in Figure 37, after tracing through two elements of 
the winding, you arrive at a commutator segment 
two removed from the one from which you started. 
The wave winding shown in Figure 35 is called a 



Figure 36.—Duplex Singly Re-entrant Lap Winding. 



Figure 37.—Duplex Singly Re-entrant Wave Winding. 


simplex winding, and the one shown in Figure 37 
is called a duplex winding. In general, the multi¬ 
plicity of a wave winding is equal to the difference 
in the numbers of the commutator segments forming 
the terminals of a number of elements, equal to one- 
half the poles, directly in series. Thus, if, after 
tracing through six elements of a wave winding for a 
twelve-pole machine, you arrive at a commutator seg- 
































































































ARMATURE WINDING 


75 


rrient three removed from the one from which you 
started, the winding is called a triplex winding. 

An inspection of Figures 38 and 39 will disclose 
the fact that all of the various elements forming each 
of these two windings are not interconnected in a 



Figure 38—Duplex Doubly Re-entrant Lap Winding. 



Figure 39.—Duplex Doubly Re-entrant Wave Winding. 


single closed circuit, as has been the case in all of the 
windings thus far discussed. If the windings shown 
in Figures 38 and 39 were removed from the arma¬ 
ture core without disturbing any of the electrical 
connections, two independent loops of wire would 
be formed in each case, and for this reason the wind¬ 
ings are said to be doubly re-entrant, that is, each 
winding closes on itself twice. 


























































































76 


ELECTRIC MOTORS 


Number of Brush Sets Required. —The number of 
brush sets required for the successful and satisfac¬ 
tory operation of a lap winding is equal to the num¬ 
ber of poles. The machine will operate with a less 
number than this, but its current capacity will be 
reduced as the useful paths through the winding 
from terminal to terminal will be reduced. 

Only two brush sets are required in the case of a 
wave winding. A number of brush sets equal to the 
number of poles is generally used, however, as com¬ 
mutation is usually better with the larger number of 
brushes. Armatures for street car motors are usually 
wave w r ound and, in the majority of cases, use only 
two brush sets. 

Number of Paths through Armature Winding .— 
The number of paths between the positive and the 
negative terminals of an armature depends upon the 
type of winding and the number of poles the machine 
has. For a lap winding, the number of paths is equal 
to the multiplicity of the winding multiplied by the 
number of poles. For example, a simplex lap-wound 
armature for a ten-pole machine will have ten cir¬ 
cuits from the positive to the negative brush ring, 
provided there are as many brush sets as poles. A 
triplex lap-wound armature for a ten-pole machine 
will have thirty circuits from the positive to the 
negative brush ring. 

The number of circuits in a wave winding is equal 
to twice the multiplicity, regardless of the number of 
poles. For example, a triplex wave winding will 
have six circuits between the positive and the nega¬ 
tive brush ring. 

Electromotive Force Generated in Armature Wind¬ 
ing. —The electromotive force generated in the arma- 


ARMATURE WINDING 


77 


ture winding of a machine depends upon the mag¬ 
netic flux entering or leaving the armature at each, 
pole, the number of poles, the number of armature 
conductors in series in each path through the arma¬ 
ture winding, and the speed, at which the armature 
is revolving. The number of conductors in series 
in each path is equal to the total number, which we 
will represent by the symbol Z, divided by the num¬ 
ber of paths, which we will represent by the symbol a. 
All of these conductors in series cut the flux under 
all of the poles once in each revolution, or the total 
flux cut by each conductor is equal to the flux per 
pole, which we will represent by the symbol <j>, multi¬ 
plied by the number of poles, which we will represent 
by the symbol p . The total flux cut by all of the con¬ 
ductors in series in each path is equal to 

Z 

— X(f>Xp 

a 


The rate at which the magnetic flux is cut per second 
is equal to the above product multiplied by the speed 
of the armature in revolutions per second, or the revo¬ 
lutions per minute divided by 60. The rate at which 
the magnetic flux is cut per second divided by 10 8 
gives the value of the induced electromotive force m 

volts, or 

p Zx<f>xpx r.p.m. 
ax 10 8 x 60 

In the above equation, r.p.m. represents the revolu¬ 
tions per minute of the armature. 




78 


ELECTRIC MOTORS 


jExample .—A four-pole machine has a simplex wave winding 
of 188 conductors; it is revolved at a speed of 1000 revolutions 
per minute; and the magnetic flux per pole is 2,000,000 max¬ 
wells. What is the value of the induced electromotive force? 

Solution .—Substituting directly in the above equation and 
remembering the value of the number of paths a is 2, gives 

188 X 2 X 10 9 X 4 X 1000 

2 £ ___ 

2 X 10 8 X 60 

= 125.3 volts 



Figure 40. —Partially Wound Armature. 



Figure 41.—Armature Coil Composed of Three Elements. 

Two-Layer Windings .—An inspection of any of 
the armature-winding diagrams in Figures 32, 33, 34, 
etc., will show that the end connections of successive 
conductors proceed alternately in opposite directions. 
It is apparent that all of the conductors in a slotted 
armature cannot lay in the same layer as in smooth 
core armatures, because of the difficulty in crossing 

























armature winding 


79 


end connections. This difficulty is overcome by 
placing one side of an element in the upper part ot 
the slot and the other side in the lower part ot the 
slot, as shown in Figure 40. One or more elements 
may be bound together, as shown in Figure 41, and 
form what is called a coil. 


CHAPTER VI 


COMMERCIAL TYPES OF DIRECT-CURRENT MOTORS 

Fundamental Principle of the Direct-Current Mo¬ 
tor. —If a wire, in which there is a direct current, be 
placed in a magnetic field in such a position that the 
center of the wire does not correspond in position to 
the direction of the magnetic field, there will be a 
force acting on the wire, due to the action of the 
current in the wire and the magnetic field upon each 
other. This force is present in the generator when 
the machine is operating and there is a current in the 
armature, and it tends to cause the armature to re¬ 
volve in the opposite direction to that in which the 
steam engine, or other prime mover, is rotating the 
armature. If there is an increase in the strength of 
the magnetic field or an increase in the value of the 
current in the wire, the position of the two with 
respect to each other remaining constant, there will 
be an increase in the force tending to move them with 
respect to each other. The value of the force be¬ 
tween the magnetic field and the wire depends upon 
their relative positions; it is a maximum when the 
center of the wire and the direction of the magnetic 
field are at right angles to each other, and a minimum 
when the center of the wire and the direction of the 
magnetic field are parallel to each other. 

Fleming’s Left-Hand, or Motor, Rule. —There is a 
definite relation between the direction of the current 

80 


COMMERCIAL TYPES 


81 


in a wire placed in a magnetic field, the direction of 
the magnetic field, and the direction of the force 
tending to move the wire with respect to the magnetic 
field. If the thumb and first and second fingers of 
the left hand be placed at right angles to each other, 
as shown in Figure 42, the second finger pointing in 
the direction of the current in the conductor , and the 
first finger in the direction of the magnetic field, then 
the thumb will point in the direction in which the 
conductor will tend to move. This simple rule is 



Figure 42.—Relation of Motion, Current and Magneto Field. 

known as Fleming’s left-hand, or motor, rule. If the 
direction of current in the wire be reversed, the direc¬ 
tion of the magnetic field remaining constant, the 
direction of the force acting on the conductor will be 
reversed; or, if the direction of the magnetic field 
be reversed, the direction of current in the wire re¬ 
maining the same, the direction of the force on the 
wire will be reversed. If, however, the direction of 
the current in the wire and the direction of the 
magnetic field are both reversed, the direction of 
the force on the wire wfill remain the same. 

Generator and Motor Interchangeable .—'The essen¬ 
tial parts of a direct-current motor are identical with 
those of a generator, namely, an armature and a 








82 


ELECTRIC MOTORS 


magnetic field. The connection of the wires on the 
surface of the armature to the external circuit is 
made by means of a commutator which serves to re¬ 
verse the current in the various parts of the arma¬ 
ture winding at the proper time so that the force 
acting on the various wires tends to produce rotation 
in the same direction, and, as a result, continuous 
rotation of the armature is produced. Any direct- 
current generator may be used as a direct-current 
motor, or vice versa, their construction being prac¬ 
tically the same. 



Figure 43.—Loop of Wire with Tw T o-Part Commutator. 


Operation of Two-Part Commutator .—If a single 
loop of wire be mounted on an axis which is at right 
angles to the direction of a magnetic field, as shown 
in Figure 43, and a current be supplied to the coil 
by means of a two-part commutator and two brushes 
which rest upon the commutator exactly opposite 
each other, there will be a force acting on the sides 
and ends of the coil. The direction of the force act¬ 
ing on any part of the coil for all the different posh 
tions the coil may occupy when it turns on the axis 




























COMMERCIAL TYPES 


83 


supporting it may be determined by a simple appli¬ 
cation of Fleming's left-hand, or motor, rule. Re¬ 
membering that the force acting on the conductor is 
always perpendicular to the direction of the magnetic 
field, we may proceed to investigate the force acting 
on the coil for various positions. The resultant force 
acting on the two ends of the coil which tends to pro¬ 
duce rotation will be zero for all positions of the 
coil. The force acting on the two sides of the coil 
will be equal in value for all positions, but the direc¬ 
tion of the force on the two sides will be exactly 
opposite each other. If the force on one side tends 
to move that side of the coil up, then the force on 
the other side tends to move that side down. The 
force acting on one side will always be up and the 
force on the other side will always be down, and 
they will remain constant in value so long as there 
is no change in the strength of the magnetic field or 
in the value of the current. These forces on opposite 
sides of the coil being in opposite directions tend to 
rotate the coil, but the tendency for rotation is not 
constant in value for all positions of the coil W lien 
the coil is in a horizontal position, the effect o± t e 
forces in tending to produce rotation is a maximum, 
because the two sides are then moving, as the coil 
rotates, perpendicular to the direction of the mag¬ 
netic field; but for any other position of the coil with 
respect to the direction of the magnetic field, the 
effect of the forces tending to produce rotation will 
be less and this effect will continue to decrease as 
Jhe coil moves from a position parallel to the field 
toward a position perpendicular to the field^ where 
the force producing rotation will be zeio. 
lation of the forces tending to rotate the coil fo 


84 


ELECTRIC MOTORS 


different positions of one complete revolution may 
be represented by a curve, as shown in Figure 44, 
in which points along the horizontal line correspond 
to different positions of the coil in degrees as meas¬ 
ured from a position perpendicular to the direction 
of the magnetic field, and the relation of the lengths 
of the vertical lines correspond to the relation be¬ 
tween the values of the forces tending to produce 
rotation for the different positions. 

Just at the instant that the coil becomes perpen¬ 
dicular to the magnetic field, the two commutator 
segments exchange positions with respect to the 



Figure 44.—Curve Showing Variation in Force Acting on Loop 
as it Revolves in a Magnetic Field. 

brushes, and as a result the current in the coil re¬ 
verses in direction. With a reversal in the direction 
of current in the coil, there is a reversal in the di¬ 
rection of the forces acting on the two sides, so that 
they tend to move across the magnetic field in opposite 
directions to what thej^ did before the current in the 
coil was reversed in direction. 

It is obvious from the above discussion that the 
force acting on the coil tends to produce a continuous 
rotation, provided the magnetic field does not change 
in direction, and that the brushes are properly placed 
on the commutator. The value of this force, however, 
fluctuates in value, it being zero when the coil is 
perpendicular to the direction of the magnetic field, 









COMMERCIAL TYPES 


8 b 


and if the coil should happen to stop in this position, 
there would be no tendency for rotation no matter 
how much current there was in the coil or how strong 
the magnetic field. Such an arrangement would not 
be at all satisfactory on account of the fluctuation 
in the turning force on the coil and also because this 
force is zero for two positions of the coil in each 
revolution. The turning force may be made nearer 
constant in value and at no time zero by means ot 
more coils and more commutator segments. 



Figure 45. —Two Loops of Wire with Four-Part Commutator. 

Multiple-Coil Armatures. If two coils of wire, 
similar to the one described in the previous section, 

with the four terminals connected to a tour-part 

”LS.«, «...».* »' “ • S' 

nected to opposite segments, as shown m Pigu e , 
then the force tending to turn the two coils will pul- 
late in value as follows: Since the two coils are at 
rLht an-L to each other, the forces acting 
on them° will likewise be at right angles 







































86 


ELECTRIC MOTORS 


each other. If the currents in the two coils 
are equal in value, and assuming they remain so 
for one complete revolution, then the forces acting 
on the two coils may be represented by two curves, 
as shown in Figure 46. Both coils do not carry 
current at the same time, since they are connected 
to independent commutator segments, and the brushes 
rest on segments exactly opposite each other. Each 
coil is connected in circuit for each revolution only 
one-half of the time, but this time is split into two 
parts and each independent connection lasts only for 



Figure 46.—Curves Showing the Relation of the Forces Acting 
on Two Loops at Right Angles to Each Other as 
They Revolve in a Magnetic Field. 

one-fourth of a revolution. Now, by properly placing 
the brushes, it is possible to get a continuous turning 
force acting on the combination of coils, and the best 
position for the brushes is such that one coil is dis¬ 
connected and the other one connected to the external 
circuit when they are making the same angle with 
the direction of the magnetic field, namely 45 degrees. 
This position of the brushes corresponds to the point 
where the curves cross each other, as shown in Figure 
46, and the resultant force acting on the two coils 
may be represented by the upper parts of the curves, 
or the shaded portion. 

By increasing the number of coils and commutator 
segments, the force acting on the coils will become 
nearer constant in value. This type of armature is 












COMMERCIAL TYPES 


87 


not satisfactory for direct-current motors as only those 
coils whose commutator segments are under the 
brushes at any particular time are in use. An arma¬ 
ture winding of this type is called an open-circuit 
winding. 

A better form of winding for direct-current mo¬ 
tors, called a closed-circuit winding, makes use of all 
of the coils all of the time except when 



Figure 47.—Simple Closed-Circuit Ring Winding. 

the two commutator segments to which a coil 
is connected are in contact with a brush or 
brushes of the same polarity. One of the 
simplest forms of closed-circuit windings is shown in 
Figure 47, which consists of a ring with four coils 
wound about it and interconnected by means of four 
commutator segments as shown in the figure. For 
convenience in referring to these coils they are desig¬ 
nated by the letters A, B. C, and D. The two coils A 
and C are short-circuited by the two brushes when 
they are in the positions shown in the figure. An 
instant later, however, coil A is in series with coil B 














































ELECTRIC MOTORS 


S8 

on the right-hand side, and coil C is in series with coil 
D on the left-hand side, and this connection remains 
until coils B and D are short-circuited by the brushes. 
An instant later coil D is in series with coil A ja. the 
right-hand side, and coil B is in series with coil C 
on the left-hand side. It is apparent that the coils 
opposite each other are short-circuited by the brushes 
at the same time when they are symmetrically ar¬ 
ranged, as in this case, and as one coil leaves the 
right-hand circuit and enters the left-hand circuit 
at the lower brush, there is a coil leaving the left- 
hand circuit and entering the right-hand circuit at 
„/ie upper brush. With this arrangement of coils and 
commutator segments, all of the coils are in circuit 
•vith the external circuit all of the time except w T hen 
they are short-circuited by the brushes. If the po¬ 
sition of the brushes is such that the coils are moving 
parallel to the magnetic field when they are short- 
oircuited, there will be no decrease in the total force 
acting on the combination tending to produce rota¬ 
tion. The direction of the current in each coil when 
it has moved from the shirt-circuited position is op¬ 
posite to what it was just before it reached this 
position, hence, the movement of the coil with respect 
to the magnetic field is reversed, that is, if it was 
tending to move up or down before short-circuited, it 
tends to move down or up after short-circuit. The 
total force tending to produce rotation at any instant 
is equal to the sum of the forces produced by each 
of the coils. When the coils are symmetrically placed 
with respect to each other, the force exerted by any 
two which are exactly opposite each other might be 
thought of as being due to a single coil having a 
number of turns equal to the sum of the turns in 


COMMERCIAL TYPES 


8% 


the two coils, The four coils in Figure 47 are sym¬ 
metrically arranged and may be treated as two coils 
instead of four. The force exerted on these two coils 
may be represented by two curves. A and B, as shown 
in Figure 48, and the total force at any time will 
be equal to the sum of the forces on the two coils, 
since they are both in circuit all the time except 
when they are short-circuited by the brushes, and 
then the force exerted by that particular coil is zero 
because it is then moving parallel to the magnetic 



Figure 48.—Curves Showing the Relation of the Forces Acting 
on Four Coils Interconnected with Four Commutator 

Segments. 

field. This total force may be represented by a third 
curve whose height at any point is equal to the sum 
of the heighths of the two curves A and B. From 
this figure it is readily seen that the force tending ta 
produce rotation is not constant in value, but it 
fluctuates between a minimum value equal to the 
maximum force produced by a single coil and a maxi¬ 
mum value equal to the combined values of the 
forces produced by the coils when they are each mid¬ 
way between their positions of minimum and maxi¬ 
mum force. The number of pulsations in the force 
per revolution may be increased by increasing the 
number of coils and commutator segments, and an 
increase in the number of pulsations per revolution 





90 


ELECTRIC MOTORS 


will result in a decrease in the difference between the 
maximum and the minimum values of the resultant 
force tending to produce rotation. Thus, with an 
increase in the number of coils and commutator seg¬ 
ments, the resultant force becomes nearer constant 
in value, and the machine is capable of developing 
a fairly constant turning effort. 

The type of armature used in the above description, 
which is called a ring type, is not used very ex¬ 
tensively at present, but, on account of the simplicity 
in its construction and the connections of the coils, 
its operation is much more readily understood than 
that of the drum type, although the fundamental 
principle of both is exactly the same and, after you 
have thoroughly mastered the operation of the ring 
type, the operation of the drum type, whether it be 
lap or wave wound, may be easily followed. 

Types of Magnetic Fields .—In the majority of 
cases the magnetic field of a motor is produced by 
electromagnets, although a magnetic field may be 
produced by powerful permanent horseshoe magnets. 
Small machines are usually bipolar, that is, they have 
one north pole and one south pole which create the 
magnetic field in which the armature rotates. These 
magnetic fields assume a number of different forms, 
a few of which are shown in Figure 49. 

In large machines it is customary to use multi¬ 
polar field magnets in which any even number of 
magnetic poles are arranged alternately around the 
armature, as shown in Figure 50, which depicts an 
eight-pole machine. 

The magnetic circuit of a motor, whose magnetic 
field is created by electromagnets, usually consists of 
five parts, see Figure 50, as follows: First, the field 


COMMERCIAL TYPES 


91 


cores G are the parts about which the coils carrying 
the magnetizing current are wound. Second, the yoke 
Y connects the field cores together at the outer end, 
as shown in the figure, and serves the double pur¬ 
pose of completing the magnetic circuit between the 






Figure 49.—Types of Two-Pole Magnetic Fields. 

field cores and of providing the necessary mechanical 
supports for the cores. In some machines there is 
no yoke in the magnetic circuit, see Figure 49. Third, 
the pole pieces P are the parts of the magnetic cir¬ 
cuit next to the armature. They are usually cut to 
conform to the curvature of the armature. They may 




































































ELECTRIC MOTORS 


92 


\ 


be formed by properly shaping the ends of the field 
cores, or they may be an entirely different piece of 
metal than the ends of the field cores, being fastened 
to the field cores by means of bolts. The surface of 
the pole pieces next to the armature is called the 
■pole face; and the projecting edges, when so con¬ 
structed, are called the pole tips. Fourth, the arma¬ 
ture core A conducts the magnetic flux between air 
gaps, and at the same time serves as a mechanical 



Figure 50.—Eight-Pole Magnetic Field. 


support for the armature winding. Fifth, the air 
gap G is the intervening space between the pole piece 
and the armature. 

When the field windings are placed on the magnetic 
circuit as shown in Figures 49a, and 49 d, the mag¬ 
netomotive force created by the current in one coil 
is in series with the magnetomotive force created by 
the current in the other coil, or the magnetomotive 
force on any magnetic circuit is that produced by the 
two coils in series. If the field windings be placed 
on the magnetic circuit as shown in Figure 49c, the 
magnetomotive force acting on any magnetic circuit 



















COMMERCIAL TYPES 


93 


will be equal to that produced by a single coil. When 
the field windings are placed as shown in Figures 
49a and 49d, only one-half as many ampere turns 
per coil will be required as would be required if the 
coils were placed as shown in Figure 49c, assuming 
the total reluctance in the two cases to be the same. 
The magnetomotive force produced by the field coils 
in Figure 49 d acts upon two magnetic circuits and, 
as a result, it is twice as effective as it would be if 
the coils were placed about the yoke between the 
poles. 

Materials Used in the Construction of the Magnetic 
Circuit of a Motor .—There are four materials that 
are commonly used in the construction of the mag¬ 
netic circuit of a motor—wrought iron, cast iron, cast, 
steel, and sheet steel. There are a number of factors 
which govern the selection of the materials to be used 
in a particular machine, such as initial cost, weight, 
efficiency demanded by purchaser, regulation, etc. 

The cheapest of the above materials is cast iron, 
but its magnetic properties are poorer than any of the 
others, so the saving in the initial cost of the iron per 
pound might be more than overbalanced by the fact 
that a larger bulk of cast iron would be required to 
form a certain magnetic circuit than would be re¬ 
quired if wrought iron, for example, were used. 
There would also be an increase in the cost of cop¬ 
per required to magnetize the magnetic circuit of 
large area, since the length of each turn would be 
more than if a better material were used or the area 
of the magnetic circuit were reduced. 

Steel, on the other hand, is the best magnetic ma¬ 
terial, and at the same time the most expensive. It 
is used where economy in weight and reduction in 


94 


ELECTRIC MOTORS 


cross-section are desired. Machines used aboard 
ships, on electric automobiles, etc., are frequently 
made of cast or laminated steel on account of the 
large reduction in weight, which is a more important 
factor than the initial cost. 

The magnetic circuits of motors are, as a rule, con¬ 
structed of more than one material. Thus, the field 
cores may be of wrought iron, as that means a saving 
in copper, since the length of the wire per turn would 
be less than if cast iron were used; the yoke may be 
made of cast iron, as its area can be made larger than 
the field cores, and this increase in area will provide 
an ample magnetic circuit and also the necessary 
mechanical strength to support the field cores. The 
armature core is usually constructed of sheet metal 
so as to reduce the eddy-current loss to a minimum; 
the pole pieces may be a part of the field cores, and 
may be cast or laminated and bolted to the ends of 
the field cores. Numerous other combinations are 
used in the construction of the magnetic circuit of a 
motor, but the above suggestions serve to illustrate 
some of the more important considerations involved 
in a proper selection of the material s for a particular 
case. 

Magnetic Leakage .—The total number of magnetic 
lines established by the field current of a motor do 
not pass through the armature core and, therefore, 
they are not all useful in the operation of the motor. 
The ratio of the total number of magnetic lines that 
are produced to the number that are actually useful 
in the operation of the motor is called the coefficient 
of dispersion. The value of this coefficient is always 
greater than one, as there are always more lines of 
force produced than are actually useful. It is always 


commercial types 


95 


desirable to have the value of the dispersion coeffi¬ 
cient as low as possible, and this is accomplished by 
constructing the magnetic circuit so it will have no 
abrupt bends, be short as possible, and have a low 
reluctance. The coefficient of dispersion can be re¬ 
duced by placing the field winding upon or near that 
part of the magnetic circuit having the greatest re¬ 
luctance and by so shaping the magnetic circuit that 
the paths conducting the magnetic flux, which is not 
useful, will have a high reluctance as compared to 
the paths conducting the useful magnetic flux. 

Excitation of Direct-Current Motors.—Direct-cur¬ 
rent motors may be divided into three classes accord¬ 
ing to the method employed in exciting the held 
magnets. These are: 

(a) Shunt motors 

(b) Series motors 

(c) Compound motors 

(a) The field winding of a shunt motor consists 
of a relatively large number of turns of small wire 
connected directly across the terminals of the ma¬ 
chine, or the circuit to which the machine is con¬ 
nected. A rheostat may be connected in series with 
the field "winding, which may be used in adjusting 
the value of the current, or no rheostat may be used 
at all and the field current allowed to vary with the 
' voltage impressed across its terminals and the change 
in resistance of the field winding, due to a change in 
its temperature. The connections of a shunt motor 
are shown diagrammatically in Figure 51. The cur¬ 
rent in the field winding is independent of the cur¬ 
rent in the armature circuit so long as a change in 
armature current produces no change in the voltage 
impressed on the shunt field winding. 


96 


EI.ECTRIC MOTORS 


(b) In the case of the series motor, the field wind¬ 
ing consists of a relatively few turns of large wire 
connected directly in series with the armature, as 
shown diagrammatically in Figure 52. The current 
in the field winding is the same as the current in 
the armature, and the strength of the magnetic field 



Figure 51.—Diagram of Shunt Motor Connections. 



Figure 52.—Diagram of Series Motor Connections. 

of the machines varies with the armature current. 
The field strength does not increase as rapidly as the 
current in the field winding, due to the fact that 
the reluctance of the magnetic circuit of the ma¬ 
chine increases with an increase in the magnetic flux. 
In some cases, there is a resistance connected in 
parallel with the series field winding and only a part 











































COMMERCIAL TYPES 


97 


of the armature current passes through the field, 
the total current dividing inversely as the resistance 
of the two branches of the divided circuit. 

(c) The field windings of a compound motor are 
a combination of the shunt and series winding, as 
shown diagrammatically in Figures 53 a and 536. The 



Figure 53a.—'Diagram Cumulative Compound Motor. 



Figure 536.—Diagram Differential Compound Motor. 

magnetic effect of these two windings may aid or op¬ 
pose each other, depending upon the manner in which 
they are connected. When the magnetizing action 
of the series and shunt field windings both act in the 
same direction about the magnetic circuit, the ma¬ 
chine is called a cumulative compound motor; and 
when the magnetizing action of the series and shunt 

























































98 


electric Motors 


field windings are in opposite directions about the 
magnetic circuit, the machine is called a differential 
compound motor. In the case of the cumulative com¬ 
pound motor, the strength of the magnetic field in¬ 
creases with an increase in series field current, since 
the two magnetizing effects act together; and in the 
case of the differential compound motor, the strength 
of the magnetic field decreases with an increase in 
series field current, since the two magnetizing effects 
act in opposite directions. 

Direction of Dotation of Machines When Changed 
from a Generator to a Motor. —The direction in which 
a direct-current generator will operate w T hen it is 
changed to a motor may be easily determined by 
the following simple relations. 

First, if the direction of the armature current and 
the direction of the magnetic flux through the magnet 
circuit of the machine both remain unchanged, or 
both are changed, when the machine is changed from 
a generator to a motor, the direction of rotation will 
be reversed. 

Second, if the direction of the armature current or 
the direction of the magnetic flux through the mag¬ 
netic circuit are either reversed, but not both, when 
the machine is changed from a generator to a motor, 
the direction of rotation will remain unchanged. 

Third, to reverse the direction of rotation of a 
motor, it is necessary to reverse either the direction 
of the armature current or the magnetic flux, but 
not both. 

If a shunt generator be changed to a motor, the po¬ 
larity of the terminals remaining the same, the direc¬ 
tion of rotation will remain unchanged, because the 
direction of the shunt field current remains the same 


COMMERCIAL TYPES 


9!> 


and the armature current reverses in direction, it 
flowing from the negative to the positive terminal 
within the generator and from the positive to the 
negative terminal within the motor. If, however, the 
polarity of the machine be reversed when it is changed 
from a generator to a motor, the direction of rotation 
will remain unchanged, because the direction of the 
shunt current is reversed and the direction of the 
armature current remains constant. 

This leads to the general statement that a shunt 
generator when changed to a motor will operate in 
the same direction, regardless of the polarity of its 
terminals, provided there is no change in the con¬ 
nection of the armature and field windings with re¬ 
spect to each other. 

If a series generator be changed to a motor, the 
polarity of the terminals remaining the same, both 
the armature current and the direction of the mag¬ 
netic flux will reverse in direction, and the direction 
of rotation will reverse. If the polarity of the ma¬ 
chine changes when it is changed from a generator to 
a motor, then the armature current and the direc¬ 
tion of the magnetic field will remain unchanged, and 
the direction of rotation will be reversed. This leads 
to the general statement that a series generator when 
changed to a motor will operate in the opposite direc¬ 
tion, "regardless of the polarity of its terminals, pro¬ 
vided there is no change in the connections of the 
armature and field windings with respect to each 

other. 

If a cumulative compound generator be changed 
to a motor without any change in the connections 
of the field windings, the machine will become a 
differential compound motor. Likewise, if the ma- 


100 


ELECTRIC MOTORS 


chine is a differential compound generator, it will 
be a cumulative compound motor. The direction of 
rotation of such a machine when changed to a motor 
will depend upon the relative effects of the series and 
the shunt field windings. For example, a differ¬ 
ential compound motor may start up under the in¬ 
fluence of the series winding and, after the shunt 
field current has had time to build up in value, the 
armature may stop and start to rotate in the opposite 
direction. 



Figure 54. —Magnetic Field of Motor Due to Field Current Alone. 

Armature Reaction in a Motor .—When there is a 
current in the armature winding of a motor there is 
a magnetizing effect produced, due to this current, 
which acts upon the main magnetic field of the motor. 
This effect is called armature reaction. The effect 
of this magnetizing action, due to the armature cur¬ 
rent, may be illustrated as follows: Take a simple 
two-pole drum armature with a number of wires uni¬ 
formly distributed over its surface and imagine it 
placed in a bipolar magnetic field, as shown in Figure 
54, which shows a cross-section through the armature 
and fields. Current is supplied to the armature 











COMMERCIAL TYPES 


101 


winding by means of two brushes which rest upon a 
commutator, and these brushes are placed in such a 
position that all of the wires on the right of a ver¬ 
tical line through the center of the armature have 
a current in them from the surface of the paper. If 
the magnetic poles have the polarity indicated in the 
figure, then the armature will tend to revolve in a 
counterclockwise direction, as indicated by the curved 
arrow. This direction of rotation may be easily de- 



Figure 55.—Magnetic Field of Motor Due to Armature 

Current Alone. 

termined by an application of Fleming’s left-hand, 
or motor, rule. The plane, marked A. C in the figure, 
which is perpendicular to the axis of the poles and 
also the sheet of paper, is called the normal neutral 
plane. This normal neutral plane is perpendicular 
to the magnetic flux when there is no current in the 
armature winding. Now imagine the field current 
of the motor is zero and that a current is sent through 
the armature winding from some outside source. The 
current in the armature winding produces a mag¬ 
netic field whose general direction through the arma¬ 
ture core is downward, as shown in Figure 55, when 















102 


ELECTRIC MOTORS 


the current is in the direction indicated in the figure. 
Since the magnetizing effects of the armature current 
and the field current are present at the same time, 
they combine and form a resultant magnetizing effect 
which produces a magnetic field whose general direc¬ 
tion is similar to that shown in Figure 56. As a re¬ 
sult of the magnetizing action of the armature cur¬ 
rent, the magnetic field of a motor is twisted in a 
direction opposite to the direction of rotation of the 



Figure 56.—Resultant Magnetic Field of a Motor. 

armature, which is just the reverse of what occurs in 
the case of the generator. This twisting of the mag¬ 
netic field results in the neutral plane, which is a 
plane perpendicular to the direction of the magnetic 
field, being moved back of the normal neutral plane, 
as shown by the line A C in Figure 56. 

Proper Position of the Brushes on a Direct-Current 
Motor .—In order that the armature produces its max¬ 
imum turning effort for a given armature current and 
magnetic field, it is necessary that the brushes be 
placed on the commutator in such a position that the 
current in the conductors on the surface of the arma¬ 
ture reverses in direction when the wires are moving 













COMMERCIAL TYPES 


103 


parallel to the magnetic field, or when they are in 
the neutral plane. It is necessary then that the 
brushes be moved backward, or opposite to the di¬ 
rection of rotation in the case of the motor, as the 
current in the armature winding increases, which 
increases the amount the neutral plane is twisted 
or moved from the position it occupies when there 
is no current in the armature winding. The brushes 
are usually moved a little farther back than the neu- 



Figure 57.—Magnetic Field of Motor Due to Armature 

Current Alone. 


tral plane, although there is a slight reduction in the 
turning effort, in order to improve commutation, as 
explained in the section on “Commutation.” The 
position occupied by the brushes is called the com¬ 
mutating plane. The position the brushes actually 
occupy with respect to the poles of the machine will 
be quite different than that indicated in the figures 
dealing with armature reaction, on account of the 
end connections of the wires to the commutator seg¬ 
ments, but the direction of the current in the differ¬ 
ent wires will be the same as indicated in the figures. 

With a change in the position of the brushes, there 
will be a change in the direction of the current in 









104 


ELECTRIC MOTORS 


some of the wires on the surface of the armature. 
Thus, if the brushes are moved opposite to the di¬ 
rection the armature tends to rotate, as shown in 
Figure 56, the direction of the current in the wires 
contained in the angle through which the brushes 
are moved will change, and the magnetic effect of 
a current in the armature will no longer be in a 
direction at right angles to the magnetizing effect of 
the field current, but in a direction similar to that 
shown in Figure 57. This magnetizing effect of the 
armature can be thought of as made up of two parts, 
one part acting perpendicular to the magnetizing 
effect of the field current, called the cross-magnetizing 
effect, and the other part acting parallel to the mag¬ 
netizing effect of the field current, called the demag¬ 
netizing effect. The demagnetizing effect of the arma¬ 
ture current tends to weaken the magnetic field of the 
motor and the cross-magnetizing effect tends to distort 
or twist the magnetic field in a direction opposite to 
the direction in which the armature rotates. 

The angle between the commutating plane and the 
normal neutral plane is called the angle of lag in the 
case of the motor, because the brushes are moved 
backward or given a lag with respect to the normal 
neutral plane, and it is called the angle of lead in the 
case of a generator, because the brushes are moved 
forward or given an angle of lead with respect to the 
normal neutral plane. 

Demagnetizing and Cross-Magnetizing Ampere- 
Turns. —The relative positions of the commutating 
planes for a generator and a motor are shown in Fig¬ 
ure 58, the full line representing the commutating 
plane of the motor and the dotted line representing 
the commutating plane of the generator. The direc- 


COMMERCIAL TYPES 


105 


tion of current in the armature wires corresponds to 
the motor connections and the direction of rotation 
will be as indicated by the curved arrow. The wires 
between the two commutating planes on one side of 
the armature can be thought of as being in series 
with the wires between the two commutating planes 
on the opposite side of the armature and forming a 
number of complete turns about the armature core. 
The remaining wires may be thought of as forming 



Figure 58.—Demagnetizing and Cross-Magnetizing Ampere- 

Turns. 

a second set of turns. The product of the turns in the 
angle between the commutating planes and the cur¬ 
rent in each of these turns gives the value of what 
is called the demagnetizing ampere-turns , because 
their effect is to produce a weakening of the mag¬ 
netic field of the machine. The product of the re¬ 
maining turns and the current they carry gives the 
value of what is called the cross-magnetizing ampere- 
turns, because they act at right angles to the mag¬ 
netizing effect of the field current of the machine. 
The turns in the angle between the commutating 
planes are called the demagnetizing, or back-turns, 
and the remaining turns are called the cross-turns. 









106 


ELECTRIC MOTORS 


Commutation .—The process of commutation can 
be explained by reference to a simplified diagram of 
the armature winding as shown in Figure 59. The 
commutator segments are marked C lf C 2 , C 3 , etc., 
while the various parts of the armature winding, 
called elements and marked 1 , 2, 3, etc., are shown 
connected in series, the terminals of these elements 
being connected to the commutator segments in regu¬ 
lar order. The position of the neutral plane is repre- 



Figure 59.—Process of Commutation. 

sented by the line A C, the direction of rotation by 
the large curved arrow, the direction of the current 
in the various elements of the winding by the small 
arrows, and the polarity of the pole, shown to the 
right, by the letter S. With a direction of current 
in the elements of the armature winding corresponding 
to that shown in the figure, the brush B must be 
negative. 

Now as the armature rotates, the commutator seg¬ 
ments in turn pass under the brush, and if the arc 
of contact of the brush on the commutator is greater 
than the width of the insulation between the com¬ 
mutator segments, which should always be the case, 





COMMERCIAL. TYPES 


107 


then an element of the armature winding will be 
short-circuited when the brush is in contact with the 
two segments to which the terminals of the element 
are connected. When an element becomes short-cir¬ 
cuited by the brush, it is no longer directly in series 
with the elements of the armature winding to its 
right or left, and the current in the element will drop 
to zero value, provided there is no electromotive force 
induced in the element or it is moving parallel to the 
magnetic field, but it does not do so instantly on 
account of a property of the element, called its in¬ 
ductance, which tends to prolong the current. As the 
armature rotates, one of the commutator segments to 
which the short-circuited element is connected moves 
out from under the edge of the brush and the short- 
circuit on the element is removed, and the element 
becomes a part of the circuit through the armature 
to the left of the brush. When the element, which 
was short-circuited, becomes a part of the left-hand 
path through the armature, it must carry the same 
current the other elements in that path carry regard¬ 
less of the value of the electromotive force being gen¬ 
erated in the element, because they are all directly 
in series. Now, if there is zero current in the short- 
circuited element, just as the short-circuit is removed 
by one of the segments moving from under the brush, 
the current in the element must increase almost in¬ 
stantly to a value equal to the current in the elements 
in the left-hand circuit through the armature. A 
property of the element—inductance—opposes this 
sudden increase in current and, as a result, there is 
a tendency for an arc to form between the edge of 
the brush and the commutator segment which is 
breaking contact with the brush until the current in 



108 


ELECTRIC MOTORS 


the element, whose short-circuit is being removed, has 
reached its proper value or the inductance of the coil 
has been overcome. This condition of affairs would 
result in a continuous sparking at the brushes, which 
would not only represent a loss but it would be 
injurious to both the commutator and the brushes. 

Sparking due to the cause just mentioned can be 
reduced and practically overcome by movipg the 
brushes back of the neutral plane. When the brushes 
are thus changed, there will be an electromotive force 
induced in the element of the winding while it is 
short-circuited and this electromotive force will be in 
such a direction as to produce a current in the ele¬ 
ment in the same direction as the current in the 
elements to the left of the brush. The induced elec¬ 
tromotive force in the element which is short-circuited 
also causes the current in the element, when it comes 
into the short-circuited position, to decrease to zero 
value in a less time than it would if there were no in¬ 
duced electromotive force in the element. The above 
results, due to the effect of the induced electromotive 
force in the short-circuited element, indicates that the 
inductance of the element is overcome while it is short- 
circuited, and there will be a current of the proper 
value already established in the element when it 
becomes a part of the left-hand circuit. Moving the 
brushes back of the neutral plane results in a de¬ 
crease in turning effort the armature is capable of 
producing, but this is more than offset by the advan¬ 
tages of better commutation. 

The winding which has been used in explaining 
commutation is perhaps the simplest form it is pos¬ 
sible to have, but the fundamental principles in¬ 
volved are practically the same in every case. 


COMMERCIAL TYPES 


109 


In certain types of lap windings the elements are 
connected to segments which are not adjacent to 
each other but may be several segments apart. In 
such a winding, it is necessary that the arc of contact 
of the brushes cover several segments in order that 
the various elements may be properly commutated. 
The time of short-circuit of the different elements 
must be such that it is possible to reverse the current 
in the element. 

In the case of wave windings, the elements are 
connected to commutator segments which are approxi¬ 
mately 360 electrical degrees apart, and instead of an 
element being short-circuited by a single brush, as in 
the lap winding, it is shorted by two brushes of the 
same polarity, these brushes being connected exter¬ 
nally by a heavy conductor, called the brush ring .. 

The brushes on a machine may be adjusted to give 
practically perfect commutation for a given field cur¬ 
rent and armature current, but, if either the field or 
the armature current, or both, change in value, there 
win be a change in the degree to which the resultant 
magnetic field of the machine is twisted, and, as a 
result, the commutation will not be as satisfactory as 
before the change. In order to have as good commu¬ 
tation as possible at all times, it would be necessary 
to move the brushes whenever there is a change in 
the position of the neutral plane. 

Commutation is improved, somewhat, by increasing 
the resistance of the short-circuited element, although 
there is a slight decrease in efficiency, due to the 
introduction of this resistance in the main armature 
circuit. When the resistance of the short-circuited 
element is increased, the current can be reversed 
in direction in a shorter time than with the lower 


110 


ELECTRIC MOTORS 


resistance. Carbon brushes have the advantage of 
giving better commutation than copper brushes, on 
account of them offering a higher resistance in the 
path of the short-circuited element than the copper 
brushes. They are sometimes copper-plated so as to 
reduce their resistance in the main circuit of the 
machine. In some cases, as in the series alternating- 
current motor, a small resistance is introduced in 
the connection between the commutator segments and 
the connections of the different elements. 

Means of Reducing Armature Reaction .—Armature 
reaction interferes with the satisfactory operation of 
the motor and it is always desirable to reduce it to 
a minimum where possible. There are a number of 
methods of bringing about a reduction in armature 
reaction, some of the more important ones” being: 

(a) By constructing the machine with a relatively long air gap 

(b) By slotting the pole cores parallel to the axis of the arma¬ 

ture core 

(c) By properly shaping the pole pieces 

(d) By placing^ a special winding in slots or openings cut in 

the pole shoes 

(e) By auxiliary magnetic poles 

(a) Increasing the length of the air gap increases 
the reluctance of the magnetic circuit and more am¬ 
pere-turns are required to produce the necessary mag¬ 
netic flux than would be required with a shorter air 
gap. The effect of the cross ampere turns on the 
armature in distorting the magnetic field is not so 
great when there is a large number of ampere turns 
required per pole as it is with a smaller number of 
ampere turns per pole, as a result, the position of 
the neutral plane of the machine remains nearer 
constant. 


COMMERCIAL TYPES 


111 


(b) Cutting slots in the pole cores parallel to the 
axis of the armature core introduces a larger reluc¬ 
tance in the path upon which the cross-magnetizing 
ampere-turns act, but does not introduce anything 



Figure 60.—Methods of Slotting Pole Cores. 


like as great a reluctance in the main magnetic ciicuit 
of the machine. Cross-sections of pole cores embody¬ 
ing this principle are shown in Figure 60. 




Figure 61.—Chamfered Pole Piece. 


(c) The shifting of the magnetic flux across the 
pole shoes of the machine can be readily reduced by 
properly shaping the pole faces so that the parts of 
the air gap where the magnetic flux tends to become 



Figure 62.—Eccentric Pole Piece. 

most, dense will have the greater reluctance. Thus the 
pole tips may be chamfered, as in Figure 61, or the 
bore of the pole faces may be made eccentric with 
respect to the armature, as in Figure 62. Additional 



































112 


ELECTRIC MOTORS 


reluctance at the pole tips may be provided by using 
a long thin tip, or, in the case of laminated poles, 
by using a stamping of the form shown in Figure 
63, in which case the laminations are built up to the 
required thickness in such a manner that the project¬ 
ing tips are on alternate sides. This construction 
may be used for the pole pieces alone and then bolted 
to a solid pole core. 

(d) A winding may be imbedded in the slots cut in 
the pole pieces and a current sent through it in 
such a direction as to produce a magnetizing effect 



Figure 63.—Laminated Pole Core and Pole Piece. 

opposite to that produced by the current in the wires 
on the surface of the armature. This winding is 
connected in series with the armature circuit and 
their magnetizing effects both vary at the same time, 
and if the two magnetizing effects neutralize each 
other for a certain load on the machine, they will 
practically neutralize for all loads, which results in 
the position of the neutral plane remaining practically 
constant and almost independent of the armature 
current. 

(e) Auxiliary magnetic poles may be placed be¬ 
tween the main magnetic poles of the machine and 
magnetized to such a polarity that they tend to coun¬ 
teract the effect of the cross-magnetizing ampere turns 







COMMERCIAL TYPES 


113 


on the armature. The windings on these poles, which 
are called interpoles, due to their position between 
the main poles, are connected in series with the arma¬ 
ture and carry all or a definite portion of the arma¬ 
ture current. This results in their magnetizing ef¬ 
fect varying directly as the armature current, just 
as the effect of the cross-magnetizing ampere turns 
-varies with the armature current, and, if the effects 
balance for one particular current, they will practi¬ 
cally balance for all other currents and the position 
of the neutral plane of the magnetic field will remain 
almost constant. . As explained in the section on 
11 Commutation, ’ ’ it is desirable to have an electromo¬ 
tive force induced in the short-circuited element, m 
order to decrease the current to zero value m a 
shorter time and to establish a current of proper 
value in the opposite direction during the time ot 
short-circuit. This induced electromotive force is 
produced by moving the brushes backward from the 
neutral plane in the case of a motor and forward 
from the neutral plane in the case of a generator 
When interpoles are used, the magnetizing effect o 
the interpole windings are usually so adjusted as to 
more than compensate for the cross-magnetizmg e - 
feet of the armature current, which results m a weak 
magnetic field being established under the interpoles. 
This weak magnetic field produces in the shor -cir¬ 
cuited element the necessary electromotive force to 
overcome the inductance of the element and there is 
no need of moving the brushes in order to have satis¬ 
factory commutation. When there is a change m the 
armature current, there is also a change in the mag¬ 
netic field under the interpoles and a larger electro¬ 
motive force is induced in the short-circuited element, 


114 


ELECTRIC MOTORS 


which readily takes care of the reversal of the larger 
current. If the direction of rotation of the armature 
is changed by reversing either the magnetic field or 
the armature current, the polarity of the interpole 
will still be such as to counteract the effect of the 
cross-magnetizing ampere turns on the armature and 
also assist in commutation as just described. 

The polarity of the interpole should always cor¬ 
respond to the polarity of the main magnetic pole 
toward which the brushes must be moved from the 
neutral plane in order to improve commutation. Thus, 
in a generator the brushes are moved forward from 
the neutral plane and the polarity of the interpole 
corresponds to the polarity of the magnetic pole to¬ 
ward which the brushes are moved; and in the motor 
the brushes are moved backward from the neutral 
plane, which results in the polarity of the interpole 
for the motor being opposite the polarity of the 
interpole for the generator, the polarity of the main 
magnetic poles being the same in each case. 

Counter-Electromotive Force .—When the armature 
of a motor is revolving in the magnetic field of the 
machine, there is an electromotive force induced in 
the wires on the surface of the armature, called con¬ 
ductors, just the same as there would be if the machine 
were operated as a generator. Since the relation be¬ 
tween the direction of motion of a wire carrying a 
current when it is placed in a magnetic field and the 
direction of the magnetic field in the case of a motor 
is opposite to what it is in the case of a generator, 
the direction of the current in the wires and the 
direction of the magnetic field remaining constant, 
the induced electromotive force in the armature wind¬ 
ing of the motor will be just the reverse of what it 


COMMERCIAL TYPES 


115 


is in the case of the generator. This induced electro¬ 
motive force acts in a direction just opposite, to the 
impressed electromotive. force which is producing the 
current in the armature winding, and, for that reason,, 
it is called a counter-electromotive force of the motor. 
The value of the counter-electromotive force Eg may 
be calculated by means of the following equation: 



Zx^xpxr.p.m. 
10 s x 60 x a 


in which E „ is the counter-electromotive force2 is 
the number of conductors on the ai mature; <f> is t e 
magnetic flux per pole; p is the number of poles*; a 
is the number of paths through the armature; r.p.m. 
is the number of revolutions per minute; 10 8 changes 
absolute units to volts; and 60 changes revolutions 
per minute to revolutions per second. 

Mechanical Output of a Motor .—The output of a 
motor in foot-pounds per second is equal to the prod¬ 
uct of the turning effort of the armature, called its 
torque , measured in pound-feet, the speed of the ar¬ 
mature in revolutions per second, and 6.2832. Repie- 
senting the torque by T and the speed by r.p.s, we 
have the following equation: 


foot-pounds per second = Tx r.p.s. x 6.2832 

Since one horsepower is equal to 550 foot-pounds per 
second then the output of the motor m horsepower 
ZZeM hp.) will be equal to the foot-pounds 

per second divided by 550, or 

bp. = (Tx r.p.s. x 6.2832)-r550 .(a) 




116 


ELECTRIC MOTORS 


If the speed is measured in revolutions per minute, 
r.p.m., then 

hp.= (Txr.p.m. x 6.2832) 33000 .. (b) 

Example .—Determine the torque in pound-feet exerted by the 
armature of a motor when the machine is developing 10 horse¬ 
power at a speed of 1000 revolutions per minute. 

Solution .—Equation (b), as given above, may be rewritten 
so as to give the value of the torque T in terms of the other 
quantities as follows: 

hp. X 33000 
r.p.m. X 6.2832 

Substituting the values in this equation of the horsepower and 
revolutions per minute given in the problem gives 

T _ 10 X 33000 
~ 1000 x 6.2832 

= 52.5+ pound-feet 

This means there would be a difference in the pull on the 
driving and slack sides of a belt of 52.5 pounds, if the radius 
of the pulley over which the belt runs was one foot. 

Torque Produced by Armature Current. — The 
torque produced by the current in the armature of 
a motor is equal to the combined effects of all of 
the conductors on the surface of the armature in tend¬ 
ing to produce rotation. The product of the total 
force, in pounds, acting on the conductors and the 
distance of the conductors from the center of the 
armature, in feet, gives the value of the torque in 
pound-feet. The value of the torque may be calcu¬ 
lated as follows: The impressed electromotive force 
E is equal to the sum of the counter-electromotive 
force E c and the resistance drop in the armature, 




COMMERCIAL TYPE 


11? 


which is equal to the product of the armature current 
I a and the resistance of the armature circuit R a . 
Putting this relation in the form of an equation gives 

E = E C + IaRa 

Multiplying the above equation by I a gives 

EI a = E c I a + Ia 2 Ra 

The term Ei a represents the total power, in watts, 
supplied to the armature of the motor, and I a Ra is 
the power lost in heat in the ohmic resistance of the 
armature circuit. It follows, therefore, that E c I a is 
the amount of mechanical power developed in the 
armature in watts. All of this mechanical power is 
not available at the shaft or pulley, for some of it is 
used in overcoming friction of the bearings, friction 
of the brushes on the commutator, windage, and the 
iron losses in the motor. 

The mechanical horsepower P developed in the ar¬ 
mature may be expressed in terms of the speed in 
revolutions per minute, r.p.m., the torque T in pound- 
feet, and the constants 6.2832, 550, and 60, as follows: 

6.2832 x r.p.m. x T 
~ 60 x 550 

The mechanical horsepower is also equal to E c I a + 
746. Placing these two values of the horsepower equal 
to each other gives 

EJ a _ 6.2832 x r.p.m. xT 
746 ~~ 60 x 550 

Solving this equation for the total torque T developed 
in the armature gives 

T- (7.05x7 a x2? c ) + r.p.m. 







118 


ELECTRIC MOTORS 


Substituting the value of E c gives 

_ 7.05 xI a xZx6xpx r.p.m . 

10 8 x a x 60 x r.p.m. 

.1175 xI a xZ x<f>xp 
“ 10 8 x a 

The only quantities in the above equation which may 
vary during the operation of the motor are the arma¬ 
ture current I a and the magnetic flux per pole <f>. 
The conductors Z, the number of poles p, and the 
number of paths a through the armature remain con¬ 
stant after the machine is constructed. 

The total torque of a direct-current motor varies 
directly as the product of the armature current, the 
magnetic flux per pole, and a constant whose value 
depends upon the construction of the motor as indi¬ 
cated above. 

Normal Speed of a Motor .—The current in the 
armature of a motor depends upon the difference be¬ 
tween the value of the impressed electromotive force 
and the counter-electromotive force divided by the 
resistance of the armature circuit. Representing the 
impressed electromotive force by E, the counter-elec¬ 
tromotive force by E c , the resistance of the armature 
circuit by R a , and the armature current by / 0 , then 

j _E-E C 

la- D 
-ti a 

Since the armature current depends upon the coun¬ 
ter-electromotive force, as shown in the above equa¬ 
tion, the motor armature will operate at such a speed 
that the difference between the impressed electromo- 





COMMERCIAL TYPES 


119 


tive force and the counter-electromotive force will 
produce sufficient current in the armature to produce 
the required torque in order that the machine may 
drive its load. Thus, with an increase in load on the 
motor there will be an increase in torque required, 
and this increase in torque will mean an increase in 
armature current if the field strength remains con¬ 
stant, but in order that the current in the armature 
increase—the resistance of the armature circuit and 
the impressed electromotive force remaining constant 
—'the value of the counter-electromotive force must 
decrease. The only factor in the equation giving the 
value of the counter-electromotive force which can 
change is the speed, since the field strength or mag¬ 
netic flux per pole <f> is supposed to remain constant 
and the other factors are governed by the construc¬ 
tion of the machine and cannot be changed without 
rebuilding. There will then be a reduction in speed, 
when the armature current must increase in value in 
order to take care of an increase in load on the 
machine. 

If the magnetic flux per pole changes at the same 
time there is a change in armature current, the change 
in speed with a change in load will be different than 
when the magnetic flux per pole remains constant. 
Thus in a series motor the field strength increases 
with an increase in armature current and, as a re¬ 
sult, the speed will have to decrease more in order to 
reduce the counter-electromotive force to its proper 
value, than in the case of the shunt motor. The speed 
characteristics of the different motors are discussed in 
detail in the next chapter. 

Starting of Direct-Current Motors .—There is no 
counter-electromotive force generated in the armature 


120 


ELECTRIC MOTORS 


winding of a direct-current motor when the armature 
is stationary; and if the armature were connected 
directly to the line, a very large current would be 
produced which would likely injure the motor. The 
value of the current just at the instant the circuit is 
closed and before there is any counter-electromotive 
force generated is equal to the impressed voltage E 
divided by the resistance of the armature circuit R a . 
The resistance of the armature circuit is usually very 
small and, as a result, there is an excessive current 
produced. By placing a resistance in series with the 
armature, the current may be prevented from rising 
to an excessive value. Now as the armature starts 
to rotate, due to the torque produced by the cur¬ 
rent in the armature winding, there will be a coun¬ 
ter-electromotive force produced in the winding which 
opposes the impressed voltage, and the current de¬ 
creases in value as the speed continues to increase. 
The speed of the motor will become constant when 
the current has been reduced to such a value, due 
to the increase in counter-electromotive force, that 
the torque produced is just ample to drive the load 
connected to the motor. Part of the resistance in 
series with the armature may be removed, however, 
before the speed has become constant, as the current 
lias decreased, due to the increase in counter-electro¬ 
motive force. When the resistance is decreased, the 
current suddenly increases but immediately starts to 
decrease if the counter-electromotive force continues 
to increase. The value of the current in the armature 
circuit of a motor when it is being started may be pre¬ 
vented from exceeding a predetermined value by de¬ 
creasing the resistance placed in series with the arma¬ 
ture at such a rate that the counter-electromotive 


COMMERCIAL TYPES 


121 


force has ample time to increase in value and replace 
the voltage drop in the series resistance. 

A simplified diagram of the connections of a start¬ 
ing resistance is shown in Figure 64. The field circuit 
of the motor must, of course, be closed when the ma¬ 
chine is being started in order that a torque be pro¬ 
duced which will cause the armature to rotate and, as 
a result of the rotation of the armature, there will 
be a counter-electromotive force generated in the 
armature winding. 



a b 

Figure 64.—Connections of Starting Resistance, a .—Correct 

Method, b.—Incorrect Method. 


Starting Boxes .—If an ordinary resistance similar 
to the one shown in Figure 64 was used in commercial 
installations of motors, there would be great danger 
of burning out the armature winding if, after the 
motor had stopped, due to the circuit to which it was 
connected becoming dead, the circuit should again 
become alive; for in that case the full line pressure 
would be connected directly across the low-resistance 
armature circuit which would result in a very large 
current. For this reason most starting resistances 
or rheostats are provided with what is called a no- 
voltage release which automatically causes the start¬ 
ing handle of the rheostat to be restored to its starting 
position when the line to which the motor is connected 
becomes dead. Very frequently these starting rheo¬ 
stats are equipped with what is called an overload 














122 


ELECTRIC MOTORS 


release which serves to disconnect the motor from 
the circuit if the current becomes excessive for any 
reason or exceeds the value for which the overload 
release is set to operate. 

In some cases a field-regulating resistance is com¬ 
bined with a starting rheostat. Such a rheostat, man¬ 
ufactured by the Cutler-Hammer Manufacturing 
Company, is shown in Figure 65. The movable arm 
consists of two parts and their outer ends move over 



Figure 65.—Motor Starting Box with No-voltage and Overload 

Release. 


separate sets of contacts. When the motor is being 
started, both parts of the arm are first moved into 
a vertical position and the lower portion is held in 
that position by the no-voltage release magnet, while 
the upper part of the arm may be moved back over the 
upper row of contacts which are connected to the 
field-regulating resistance. 

Starting rheostats used in connection with series 
motors on street cars are not provided with a no- 
voltage release as the motorman is supposed to return 
the controller handle to the starting position when 
the line becomes dead. An overload on the motors 





COMMERCIAL TYPES 


123 


is prevented by means of a circuit-breaker. In some 
cases the motorman must hold the controller hand in 
the various positions against the action of a spring 
which will restore the handle to its starting position 
should the motorman happen to let go the handle. 


CHAPTER VII 


SPEED CONTROL, OPERATING CHARACTERISTICS, 
AND TESTING OF DIRECT-CURRENT MOTORS 

Methods of Regulating the Speed of Direct-Current 
Motors. —The speed of a direct-current motor may be 
regulated by any one, or certain combinations of the 
following methods: 

(A) Change in magnetic flux per pole 

(B) Change in voltage impressed upon the armature terminals 

(C) Change in brush position 

(D) Series-parallel connections of motors, as in railway work 

Regulating Speed by Change in Magnetic Flux .— 
There are two distinct methods used in changing the 
magnetic flux per pole in a motor: 

(a) By changing the ampere turns producing the magnetic 

flux 

(b) By changing the reluctance of the magnetic circuit 

(a) The current in the field wdnding of a shunt 
motor is equal to the voltage acting on the field circuit 
divided by the resistance of the field circuit. If a 
suitable resistance be connected in series with the 
shunt-field winding, as shown in Figure 66, the cur¬ 
rent in the circuit may be varied from a very low 
value to be a maximum value equal to the impressed 
voltage divided by the resistance of the field winding 
alone. 

The current in the field winding of a series motor 
varies as the armature current, and the two are usu- 

124 


'SPEED CONTROL, OPERATING AND TESTING 125 

ally equal in value. A variable resistance, however, 
may be connected about the series, as shown in Fig¬ 
ure 67, and the portion of the total current which 
passes through the series field varied by adjusting 
the variable resistance. In some cases the field coils 
are so arranged that they may be connected in series 



Figure 66—Connection of Field Rheostat in Field of Shunt 

Motor. 

in parallel or in a combination of series and parallel 
by means of a suitable controller, which results in 
each coil carrying a different part of the total current 
for the different connections. 

The field strength of the compound motor depends 
upon the combined action of the shunt and the series 



Figure 67.—Connection of Variable Resistance in Parallel with 

Field of Series Motor. 

windings. The current in either of these windings 
may be varied as described above, and, as a result, 
there will be a change in the strength of the magnetic 
field or flux per pole. 

If the flux per pole in a direct-current motor be 
decreased in value, there will be an increase in speed 
for the following reason. The decrease in flux per 


















126 


ELECTRIC MOTORS 


pole results in a decrease in counter-electromotive 
force and the current in the armature immediately 
increases, which results in a greater torque being 
produced than is required to drive the load and 
the speed of the motor increases. The increase in 
speed causes the counter-electromotive force to in¬ 
crease, which reduces the value of the current; and 
when the current has decreased to such a value that 
the torque being developed is equal to that required 
to drive the load, the speed will become constant. 
The change in the flux per pole resulting from a 
change in the current in the field winding will depend 
upon the degree to which the iron of the magnetic 
circuit of the motor is saturated. If the magnetic 
circuit is being worked at a point Avell up on the 
magnetization curve, there must be a relatively large 
change in field current to produce a comparatively 
small change in magnetic flux. 

There is a limit, however, to the amount you can 
weaken the magnetic field of a motor as the armature 
reaction, due to a given armature current, increases 
with a decrease in field strength, which results in 
poor commutation. The effect of armature reaction 
can be reduced in a number of different ways, as 
explained in Chapter VI, but the results obtained 
when interpoles are used are more satisfactory than 
by any of the other methods. Without interpoles, it 
is impossible to vary the speed of a motor whose 
normal speed is about 1000 revolutions per minute 
more than two or three hundred revolutions by chang¬ 
ing the field strength without trouble due to spark¬ 
ing, while the minimum and maximum speeds of an 
interpole motor may be in the ratio of one to six 
without serious sparking. 


SPEED CONTROL, OPERATING AND TESTING 127 

(b) The magnetic flux per pole may be reduced 
by increasing the reluctance of the magnetic circuit, 
there being no change in the ampere turns per pole. 
This is accomplished in the case of a motor manufac¬ 
tured by the Stow Manufacturing Company, in the 
following way: The field cores are hollow and pro¬ 
vided with movable iron cores. The movable iron 
cores are mechanically connected so that their position 
within the hollow cores can be adjusted by means of 
a hand wheel on top of the machine. By moving them 
toward or away from the pole pieces, there will be a 
decrease or increase in the reluctance of the mag¬ 
netic flux per pole which will produce a change in 
the speed. 

In the Lincoln adjustable speed motor, the arma¬ 
ture core is tapered and also the field bore, so that 
as the armature is moved endwise by means of a 
special mechanical device, the length of the air gap 
is increased or decreased and the magnetic flux per 
pole changed. In small motors of this type the 
ratio of the maximum and the minimum speeds may 
be as much as ten to one. 

Controlling Motor Speed by Varying Voltage Im¬ 
pressed upon the Armature Terminals. —The voltage 
impressed upon the terminals of the motor may be 
varied by any one of the following methods: 

(a) By placing a resistance in series with the armature 

(b) By operating the motor on a multi-voltage system 

(c) By varying the voltage of the generator supplying cur¬ 

rent to the motor 

(a) If a rhedstat be placed in series with the 
armature of a motor, as shown in Figure .68, the volt¬ 
age across the armature terminals may be varied by 
changing the resistance of the rheostat. A change 




128 


ELECTRIC MOTORS 


in impressed voltage on the armature will mean a 
change in speed, because there will be a change in 
the value of the counter-electromotive force required. 

This method of controlling the speed is not at all 
efficient on account of the loss in the series resistance. 



Figure 68.—Resistance in Series with Armature Circuit. 

The voltage impressed upon the armature will change 
with a change in armature current, which results in a 
greater change in speed with change in load than 
would occur if the voltage over the armature remained 
Constant. 



Figure 69.—Multi-voltage Method of Speed Control. 

(b) In the multi-voltage method of speed control, 
there are several different voltages available from 
which the motor may be operated. Thus, as shown 
in Figure 69, the voltage between the main lines 
is subdivided by means of a balancer set which 
makes it possible to impress upon the armature a 


































SPEED CONTROL, OPERATING AND TESTING 129 

number of different voltages. The motor will have 
a definite speed for each of these voltages and it 
will be practically constant for all loads when the 
controller resistance in series with the armature is 
all out of circuit. The shunt field winding is usually 
connected permanently to the main line, and the 
field strength remains practically constant for all 
connections of the armature. The controller used in 
changing the armature connections is quite similar 
to an ordinary railway motor controller. 



Figure 70.—Ward-Leonard System of Speed Control. 


It is possible, with the arrangement indicated in 
Figure 69, to impress six different voltages upon the 
armature of the motor, namely, 40, 70, 110, 150, 180, 
or 220 volts, giving six different speeds. Speeds 
intermediate between those given by the above volt¬ 
ages may be obtained by varying the strength of the 
magnetic field. This system is extensively used in 
operating machine tools, but it has the disadvantage 
of requiring quite a large investment in the balancer 
and extra copper required in the distributing circuits. 

(c) The speed of a motor may be controlled by 
varying the voltage of the generator supplying cur¬ 
rent to the motor, as shown in Figure 70, which 


























130 


ELECTRIC MOTORS 


shows diagrammatically what is known as the Ward- 
Leonard system. The motor M, whose speed is to be 
controlled, is separately excited from the main circuit 
and its armature is directly connected to the termi¬ 
nals of the armature of an auxiliary generator G. 
The generator G is driven by a shunt motor M lf 
which takes its power from the main line. It is not 
necessary that a motor be used in driving the gen¬ 
erator G, as any other form of prime mover may 
be used. The field of the generator G is connected 
to the main line through a reversing switch, and a 
rheostat is in series by means of which the voltage 
may be adjusted from zero to a maximum value in 
either direction. With this combination, it is pos¬ 
sible to get a very uniform variation in the voltage 
impressed upon the motor and the operation will be 
very satisfactory. This method is especially useful 
where very uniform gradation of speed in either 
direction is required, as in the operation of the 
turrets on battleships, etc., but it is expensive because 
of the additional equipment. 

Controlling the Speed of a Motor by Varying the 
Position of the Brushes .—If the brushes of a direct- 
current motor be moved from the neutral plane of 
the magnetic field, there will be a change in speed 
for the following reasons. The counter-electromotive 
force between the brushes of a motor is maximum 
when the brushes are in the neutral plane, because 
the electromotive forces induced in all the conductors 
in series in the various paths through the armature 
winding are all acting in the same direction. If the 
position of the brushes be changed, assuming the mag¬ 
netic flux per pole and the speed remains constant, 
then the counter-electromotive force between the 


SPEED CONTROL, OPERATING AND TESTING 131 


brushes will be reduced and the current in the arma- 
tuer winding will be increased, which causes an in¬ 
crease in torque and, hence, an increase in speed. 
The magnetic flux pole and the position of the neu¬ 
tral plane do not remain constant when the position 
of the brushes is changed, even though the arma¬ 
ture current remains constant, as there is a change 
in the effect of armature reaction. If the brushes 
are moved back of the neutral plane, there is an in¬ 
crease in the demagnetizing ampere turns and a 
decrease in the cross-magnetizing ampere turns, as¬ 
suming the armature current does not change in 
value, causing a decrease in magnetic flux per pole 
and also a decrease in the distortion of the magnetic 
field. When the brushes are moved forward of the 
neutral plane, there will be a decrease in the demag¬ 
netizing ampere turns on the armature and an in¬ 
crease in the cross-magnetizing ampere turns, assum¬ 
ing the armature current does not change in value, 
causing an increase in magnetic flux per pole and also 
an increase in distortion of the magnetic field. An 
increase in magnetic flux per pole alone means a 
decrease in speed or a decrease in magnetic flux per 
pole an increase in speed, likewise, a change in brush 
position alone means an increase in speed as they 
are moved from the neutral plane. It is readily seen 
that the change in speed resulting from a change in 
brush position will depend upon the change in mag¬ 
netic flux per pole caused by the brushes being 
changed and also the relative relation of the brush 
position and the neutral plane before and after the 
change is made. Usually there is an increase m 
speed as the brushes are moved in either direction 
from their normal position, but in some cases there 


132 


ELECTRIC MOTORS 


may be first a decrease and then an increase in speed 
when the brushes are moved in advance of the neutral 
plane, especially if the motor is carrying quite a 
large load and the brushes are moved from a position 
determined when the motor was operating without 
load. This method of varying the speed of a motor 
is not at all practical, as excessive sparking usually 
results when the brushes are moved very far from 
their proper, position. In the case of the interpole 
motor the brushes must always be placed in a definite 
position on the commutator in order that the parts 
of the winding undergoing commutation may be in 
the proper position with respect to the interpoles. 
This position is usually such that the motor may be 
operated in either direction equally well. 

The brushes, in the case of an ordinary motor, 
may be placed in the neutral plane by moving them 
back and forth, at the same time noting the changes 
in speed, and the position giving minimum speed will 
correspond to the neutral plane, no load on the motor. 
The brushes are usually moved back a slight amount 
of the minimum speed position for no load, so that 
their position with respect to the neutral plane will 
be nearer correct under load conditions than it would 
be if they were not moved. 

Control of Motor Speed by Series-Parallel Con¬ 
nections .—The control of motors by the series- paral¬ 
lel method depends upon a change in voltage over 
the armatures of the different motors which is pro¬ 
duced by a change in connections of the motors to¬ 
gether with a resistance arranged so it can be con¬ 
nected in circuit and varied in value. This method 
of control is confined almost entirely to series rail¬ 
way motors where there are two or more on each car. 


SPEED CONTROL, OPERATING AND TESTING 


133 


In the case of cars having two-motor equipment, 
the two motors and the starting resistance are all 
connected directly in series when the starting handle 
is thrown to the first position. As the starting handle 
is moved from the first position to the second, and 




Figure 71.—Motors in Series. 



so on, the resistance in circuit is reduced in value 
until the two motors are connected directly in series 
with the full voltage across the combination. A 
further movement of the starting handle connects 
the two motors in parallel and a resistance in series 



Figure 72.—Motors in Parallel. 


with them; this resistance is then cut out as the start¬ 
ing handle is moved on toward its last position when 
the motors are in parallel with full voltage impressed 
upon each. A good idea of the operation of a two- 
motor equipment may be obtained by reference to 
Figures 71 and 72. In Figure 71 the motois are in 
series and in Figure 72 they are in parallel. 


























134 


ELECTRIC MOTORS 


When four-motor equipments are used, the motors 
are usually connected in parallel in pairs and the 
two pairs $re then connected in series-parallel just 
as though each pair were a single motor. The series- 
parallel method of control is more economical than 
if each motor had its own individual starting resist¬ 
ance, or if all the motors were in parallel and pro¬ 
vided with a single starting resistance. 

The successive changes in the starting resistance 
and the change in the connections of the motors are 
accomplished by means of a device called a controller. 
The two positions of the controller in which the mo¬ 
tors are directly in series or directly in parallel, 
without any resistance in circuit in either case, are 
called running points , because in these positions there 
is no loss in the starting resistance. All other posi¬ 
tions of the controller, except those where the change 
from series to parallel connection takes place, are 
called resistance points. 

There are a number of different types of railway 
motor controllers on the market and they perform 
their functions in a little different manner. Thus, 
type B controllers are those in which rheostats are 
used without any series-parallel arrangement. This 
type of controller is generally used with single-motor 
railway equipments, or for cranes and hoists. Type 
K controllers are for series-parallel control of two or 
more series motors and are so constructed that the 
power circuit is not broken when the change is made 
from series to parallel connection. Type L controllers 
are also for series-parallel control of two or more 
series motors and are so constructed that the power 
circuit is broken when the change is made from 
series to parallel connection. Type B controllers 


135 


SPEED CONTROL., OPERATING AND TESTING 

have the customary power circuit connections and, in 
addition, make use of the motors as generators in 
operating magnetic brakes of the axle or track type. 

All of the controllers given above, with the excep¬ 
tion of certain R types, are provided with two han¬ 
dles—one for the control of the resistance and motor 
connections and the other for the reversal of the direc¬ 
tion of the motion of the car. These two handles are 
usually mechanically interconnected in such a way 
that the reversing handle cannot be moved unless 
the main control handle is in the “off” position, and 
likewise the main handle cannot be moved unless 
the reversing handle is in either the forward, or re¬ 
verse, position. 

The controllers described thus far will work in the 
case of a single car, or a motor car and trailer, but 
where several motor cars and trailers are to be oper¬ 
ated as a train, a multiple-unit type of control, such 
as the type M, must be used. The controller in this 
case carries only a small auxiliary current inde¬ 
pendent of the current in the motor and this current 
operates electromagnets which, in turn, operate de¬ 
vices called contactors that control the main cur¬ 
rent. The current operating the electromagnets of 
the contactors may be controlled from any number 
of different positions, depending upon the number 
of controllers connected to the circuit. This control 
circuit is continuous through the different cars form¬ 
ing the train by means of a flexible multiple con¬ 
ductor connection between the different cars. This 
type of control is frequently used on single cars, as 
it eliminates the necessity of carrying the heavy mo¬ 
tor currents through the controller in the motor- 
man’s cab. 


136 


ELECTRIC MOTORS , 


Operating Characteristic of Direct-Current Motors . 
—There are three principal classes of service in the 
commercial application of motors and these classes 
may be characterized as follows: 

(a) Constant speed 

(b) Adjustable speed 

(c) Variable speed 

(a) Constant-speed motors are those which main¬ 
tain a practically constant speed at all loads, when 
operated on a constant-voltage circuit. Motors of 
this kind are used in driving machinery whose speed 
is to remain practically constant at all times, as 
line shafting. 

(b) Adjustable-speed motors are those whose speed 
can be fixed at any one of a large number of values 
between a minimum and maximum value, and, after 
such an adjustment is made, the speed will remain 
practically constant for all loads not exceeding the 
capacity of the machine, the impressed voltage re¬ 
maining constant. Motors of this kind are used, for 
example, for individual drives for machine tools. 

(c) Variable speed motors are those whose speed 
changes, due to a change in load without any ad¬ 
justment w r hen operating with a constant impressed 
voltage. Motors of this kind are used where it is 
desirable to have their speed decrease as the load 
they are operating increases, as in street-railway work, 
hoisting machinery, and rolling mills. 

In order to completely understand the operation of 
the different types of direct-current motors, it is nec¬ 
essary to get a mental picture of the relation be¬ 
tween speed, torque, and load current. These rela¬ 
tions determine what are called the operating or com- 


SPEED CONTROL, OPERATING AND TESTING 


137 


mercial characteristics and they will be discussed in 
the following sections: 

Characteristics of the Shunt Motor .—When the 
shunt motor is operated with a constant impressed 
voltage and constant resistance in the field circuit, 
its speed will usually decrease with an increase in 
load or armature current, as shown in Figure 73. If 
the decrease in field strength, due to armature reac- 



Figure 73.—Characteristics of Shunt Motor. 


fcion, causes the required decrease in counter-electro¬ 
motive force as the armature current increases, then 
the speed will remain practically constant. There will 
be a smaller decrease in speed in a shunt motor 
having a low armature resistance than in the case 
of one having a relatively high armature resistance. 

The torque of a shunt-motor increases with an in¬ 
crease in armature current and would vary directly 
as the armature current if the field strength of the 
machine and the position of the brushes with respect 
to the neutral plane of the field remained constant. 
The total torque in the case of a shunt motor is 

























138 


ELECTRIC MOTORS 


related to the armature current as shown in Fig¬ 
ure 73. 

Characteristics of the Series Motor .—The speed of 
a series motor decreases with an increase in armature 
current, which causes an increase in magnetic flux 
per pole and also a decrease in the required counter¬ 
electromotive force. The speed is a maximum at no 
load and theoretically it would be infinite. The 
relation of speed to armature current for the series 
motor is shown in Figure 74. 



Figure 74.—Characteristics of Series Motor. 


The torque of a series motor increases more rap¬ 
idly with an increase in armature current than in the 
case of the shunt motor, because the magnetic flux 
per pole is increasing at the same time the armature 
current is increasing. If the magnetic flux per pole 
increased directly as the armature current, then the 
torque would vary as the square of the armature 
current, since the torque is proportional to the prod¬ 
uct of the magnetic flux per pole and the armature 
current. The magnetic flux per pole, however, does 
not increase as rapidly as the armature current, due 























SPEED CONTROL., OPERATING AND TESTING 139 


to the magnetic circuit becoming saturated, and, 
hence, the torque increases less and less rapidly as 
the armature current increases in value. The rela^ 
tion of the total torque to the armature current for 
the series motor is shown in Figure 74. 

Characteristics of the Compound Motor .—-When the 
shunt and series field windings of a compound motor 
are connected so that their magnetizing effects both 
act in the same direction, it is called a cumulative 












/ 






















»z 







Sfce i 

<£ 

























































7 



Cu 

'ren 







Figure 75 .—Characteristics of Cumulative Compound Motor. 

compound motor; and if the magnetizing effects of 
the two field windings oppose each other, it is called 

a differential compound motor. 

The speed of a cumulative compound motor de¬ 
creases more rapidly with an increase in armature 
current than in the case of the shunt motor, because 
the magnetic flux per pole is increasing with an in¬ 
crease in armature current which passes through the 
series field winding. The relation of speed to ai ma¬ 
ture current for the cumulative compound motor is 
shown in Figure 75. 

The torque of a cumulative compound motor m 












































140 


ELECTRIC MOTORS 


creases more rapidly with an increase in the armature 
current than in the case of the shunt motor, because 
the magnetic flux per pole is increasing, due to the 
acting of the armature current in the series field wind¬ 
ing. The relation of torque to armature current for 
the cumulative compound motor is shown in Fig¬ 
ure 75. 

The speed of a differential compound motor does 
not decrease as much with an increase in armature 



Figure 76.—Characteristics of Differential Compound Motor. 

current as in the case of the shunt motor, because 
the magnetic flux per pole is decreased, due to the 
action of the armature current in the series field 
winding. The speed may remain practically constant, 
it may decrease a slight amount, or it may increase 
with an increase in armature current, depending upon 
the effect of the series field winding in changing the 
value of the magnetic flux per pole. The relation 
of speed to armature current for a differential com¬ 
pound motor is shown in Figure 76. 

The torque of a differential compound motor does 
not increase as rapidly with an increase in the arma- 






















SPEED CONTROL, OPERATING AND TESTING 141 


ture current as in the case of the simple shunt motor, 
because the magnetic flux per pole is decreased, due 
to the action of the current in the series field winding. 
The relation of torque to armature current for the 
differential compound motor is shown in Figure 76. 

The differential compound motor is seldom used in 
practice for the reason that the slightly drooping 
speed characteristic for the simple shunt motor meets 
practically all of the requirements of constant speed. 
Such motors are likely to start up in the wrong direc¬ 
tion when the starting handle of the starting rheostat 
is turned to the first notch, because the shunt does 
not build up to its maximum value instantly and, 
hence, the direction of the magnetic flux will be gov¬ 
erned by the current in the series field. When the 
shunt current has had time to build up, the mag¬ 
netic flux per pole will be reversed and, hence, the 
direction of rotation of the armature. 

Losses in Direct-Current Motors .—The losses in 
motors may be divided into two main groups: 

(a) Electrical losses 

(b) Stray-power losses 

(a) The electrical losses occur in any part of the 
motor carrying a current, and the value of this loss, 
in watts, for any circuit is equal to the current in 
the circuit squared times the resistance of the cir¬ 
cuit. Thus, if the current in the armature be rep¬ 
resented by I a and the resistance of the armature by 
R a , then the electrical loss in the armature will be 
given by the following equation: 

electrical loss in armature = I a z D a watts 


142 


ELECTRIC MOTORS 


The electrical loss in any other part of the motor 
may be calculated as indicated above. 

(b) The stray-power losses consist of: 

(1) Hysteresis and eddy-current losses, chiefly in 
the armature, called iron losses. 

(2) Friction loss at the bearings and the brushes, 
and air friction, or windage, as it is called, 
due to the fan-like action of the different parts. 

The stray-power losses cannot be calculated with 
the same degree of accuracy as the electrical losses; 
but they can, however, be quite accurately determined 
by experiment for a given machine. 

Efficiencies of a Direct-Current Motor .—There are 
three efficiencies for a direct-current motor, namely, 

(a) Efficiency of conversion 

(b) Mechanical efficiency 

(c) Commercial efficiency 

(a) The efficiency of conversion is equal to one 
hundred times the ratio of the total mechanical power 
developed to the total electrical power supplied. The 
total mechanical power developed in a motor is equal 
to the input minus the electrical losses, or to the out¬ 
put plus the stray-power losses. The input to the 
motor in watts is equal to the product of the voltage 
E impressed upon the armature terminals and the 
total current supplied to the motor, or 


input -E x / watts 


SPEED CONTROL, OPERATING AND TESTING . 143 


The power output of the motor in watts is equal to 
the horsepower (hp.) delivered by the motor multi¬ 
plied by 746, or 


output = hp. x 746 watts 


total power developed = (E x 7) - electrical losses 

or 


= (hp. x 746) + stray-power 
losses 


efficiency of 


conversion = 


El - electrical losses^ 1 nn 
ExI 


746 x hp. + stray-po wer losses w 00 
ExI 


(b) The mechanical efficiency of a motor is equal 
to one hundred times the ratio between the output 
of the motor and the total mechanical power de¬ 
veloped. 

_ 746xhp. _ x 100 

mechanical efficiency- 74.5 hp. + stray-power loss 

or „ , 

_ 746 xhp ~ -x 100 

ExI- electrical losses 


(c) The commercial efficiency of a motor is equal 
to one hundred times the ratio of the output to the 

input. 


commercial 


efficiency = 


746xhp. x ioQ 

ExI 











144 


ELECTRIC MOTORS 


The commercial efficiency is the most important of 
the three, as it includes all the losses in the machine 
and is of more interest to the purchaser than either 
of the other efficiencies. 

Determining the Commercial Efficiency by Prony 
Brake .—The commercial efficiency of a motor may be 
determined by measuring the electrical input by 
means of a voltmeter and ammeter or by means of a 
wattmeter, and at the same time measuring the me¬ 
chanical output. The mechanical output of the motor 



may be determined by means of a Prony brake. The 
construction and operation of this brake can best 
be explained by reference to Figure 77. The brake 
proper consists of two parts A and B, that are held 
together by two bolts, C and D. The bolts are pro¬ 
vided with two hand wheels E and F by means of 
which the pressure of the two parts of the brake A and 
B upon the pulley G can be varied. An arm H is 
attached to the brake and extends out to one side at 
right angles to the shaft upon which the pulley G 
is mounted. When the brake is in use, the outer end 
of the arm H rests upon the platform of a pair of 
scales or it is hung from a spring balance. The torque 
















SPEED CONTROL, OPERATING AND TESTING 145 


produced by the armature driving the pulley G, in 
pound-feet, is equal to the net reading of the scales 
at the end of the arm E , in pounds, multiplied by 
the horizontal distance L, in feet, from the centei 
of the shaft to the point where the end of the arm 
E rests upon the scales. The net scale reading is 
obtained by subtracting from the scale readings foi 
the different loads the scale reading when the pulley 
is not revolving. Representing the net scale reading 

by W, then 

T=WxL pound-feet 

and the output in horsepower will be equal to 

6.2832x Txr.p.m. 
hp -" 33000 

6.2832 xWxLx r.p.m. 

33000 


Substituting this value of the output in horsepower 
in the equation for commercial efficiency gives 

746 x 6.2832 x W x L x r.p.m. v , nn 
commercial efficiency- £x/x 33000” 


14.203 x W x L x r.p.m. 

= ' Wxl 

Vxamvle —In testing a direct-current motor by means of a 
Prony brake, the net scale reading was 55 pounds, the lever 
Pr0 L «?„ brake was 2 feet, and the motor was running at a 
of 1000‘r.p.m. What was its commercial efficiency if the 

the equation for comme, 

cial efficiency gives 14.203 X 55 X 2 X 1000 

commercial efficiency = - 220 X 80 

= 88.7 + per cent 













CHAPTER VIII 


CAKE AND OPERATION OF DIRECT-CURRENT MOTORS 
AND DIRECT-CURRENT MOTOR TROUBLES 

The following instructions relative to the care and 
operation of direct-current machines are reproduced 
mainly from the “General Rules” of the Westing- 
house Electric and Manufacturing Company, Pitts¬ 
burgh, Pennsylvania. 

General Rules .— (1) Leave all switches open when 
machine is not running. 

(2) At all times keep the generator or motor clean 
and free from oil and dust, especially from copper 
or carbon dust. The finest machines and the most 
expensive plant may be shut down by accident if they 
do not have protection and care. The insulation must 
be kept clean and dry. Oil and dirt in the insulation 
are as much out of place as grit or sand in a cylinder 
or bearing. In a direct-connected unit, oil may splash 
from the driving machine, or work along the shaft 
to the insulation and cause a burn-out if the attendant 
has not provided the necessary protection. With high 
voltage machines a small accumulation of dust on the 
windings may be the cause of serious burn-out. In 
stations of sufficient size to warrant the expense, it is 
advisable to install an air pump with a piping system 
so distributed that a short section of hose will enable 
the attendant to reach all parts of the winding on 
any machine to blow out the dust. The pressure used 

146 


CARE AND OPERATION 


147 


in such service should not exceed 25 pounds pei 
square inch, as a high pressure may lift the insula¬ 
tion wrappings on the windings and blow dust inside 
the coils. Always allow the accumulation of water 
in the pipes to be blown out before turning the air 
blast on the machine. 

(3) Keep small pieces of iron, and bolts, and tools 
away from the frame. Any such fragment attracted 
to the pole of a field magnet may jam between the 
armature and the pole and cause serious damage. _ 

(4) Occasionally give the machine a thorough in¬ 
spection. The higher the voltage of the generator 
or motor, the oftener this should be done. 

Brushes .—The position of the brushes on a direct- 
current machine should be on, or near, the no-load 
neutral point of the commutator. The no-load neu¬ 
tral point on all standard machines is m line with 
the center of the pole. Generators should have the 
brushes set a little in advance of this neutral point 
In other words, the brushes of the generator should 
be given a slight “forward lead” in the direction 
of rotation of the armature. Motor brushes should 
be set somewhat back of the neutral point. The 
“backward lead” in this case is approximately equal 
to the forward lead on generators. The exact position 
in either case is that which gives the best commu¬ 
tation at normal voltage for all loads. In no case 
should the brushes be set so far from the neutral 
point that it will cause dangerous sparking at no- 

l0 The ends of all brushes should be fitted to the com¬ 
mutator so that they make good contact over their 
entire bearing face. This can be most easily accom¬ 
plished after the brush holders have been adjusted 


148 


ELECTRIC MOTORS 


and the brushes inserted. Lift a set of brushes suffi¬ 
ciently to permit a sheet of sand-paper to be inserted. 
Draw the sand-paper back and forth under the 
brushes in the direction of rotation, being careful to 
keep the ends of the paper as close to the commutator 
surface as possible and thus avoid rounding the edges 
of the brushes. It will be found that by this means 
a satisfactory contact is quickly secured, each set 
of brushes being similarly treated in turn. If the 
brushes are copper plated, their edges should be 
slightly beveled, so that the copper does not come 
in contact with the commutator. 

Commutator. — The commutator should be kept 
smooth by the occasional use of No. 00 sand-paper. 
A small quantity of high grade light body oil should 
be used as a lubricant. The lubricant should be 
applied to high-voltage generators by aid of a piece 
of cloth attached to the end of a dry stick. If the 
commutator gets “out of true” it should be turned 
down. 

Sparking .—Sparking of the brushes may be due to 
any one of the following causes: 

(a) The machine may be overloaded. 

(b) The brushes may not be set exactly at the point of com¬ 

mutation. A position can always be found where there 
is no perceptible sparking, and at this point the brushes 
should be set and secured. 

(c) The brushes may be wedged in the holders. 

(d) The brushes may not be fitted to the circumference of the 

commutator. 

(e) The brushes may not bear on the commutator with sufficient 

pressure. 

(f) The brushes may be burnt on the ends. 

(g) The commutator may be rough; if so, it should be 

smoothed off. 


CARE AND OPERATION 


149 


(h) A commutator bar may be loose, or may project above 

the others. 

(i) The commutator may be dirty, oily, or worn out. 

^j) Unsuitable carbon in the brushes. 


These are the more common causes, hut sparking 
may be due to an open circuit or loose connection m 
the armature. This trouble is indicated by a bright 
spark which appears to pass completely around the 
commutator and may be recognized by the scarring 
of the commutator at the point of open circuit, 
a lead from the armature winding to the commutator 
becomes loose or broken, it will draw a bright spark 
as the break passes the brush position. This trouble 
can be readily located, as the insulation on each side 
of the disconnected bar will be more or less pitted. 

The commutator should run smoothly and true r 


with a dark, glossy surface. 

Heating of Field Coils .—Heating of held coils may 

develop from any of the following causes: 


(a) Too low speed. 

(b) Too high voltage. , . _ , 

(c) Too great forward or backward lead of brushes. 

(d) Partial short circuit of one coil. 

(e) Overload. 

Heating of Armature .—Heating of the armature 
may develop from any of the following causes: 


(b) Partiafshort-lTreuit of two coils will heat the two particu- 

lar coils affected. . . „ 

(e) Short circuits or grounds on armature, or commutator. 

Heating of Commutator— Heating of the commu¬ 
tator may develop from any of the following causes: 


150 


ELECTRIC MOTORS 


(a) Overload. 

(b) Sparking at the brushes. 

(c) Too high brush pressure. 

(d) Lack of lubrication on commutator. 

Bearings .—Watch the bearings carefully from the 
time the machine is first started until the bearings 
are warmed up, then note the oil level. The expan¬ 
sion of the oil due to heat and foaming raises the 
level considerably during that time. The oil should 
be renewed about once in six months, or oftener if 
it becomes dirty or causes the bearings to heat. 

The bearings must be kept clean and free from 
dirt. They should be examined frequently to see that 
the oil supply is properly maintained and that the 
oil rings do not stick. Use only the best quality of 
oil. New oil should be run through a strainer if it 
appears to contain any foreign substances. If the oil 
is used a second time it should first be filtered and, 
if warm, allowed to cool. 

If a bearing becomes hot, first feed heavy lubricant 
copiously, loosen the nuts on the bearing cap, and 
then, if the machine is belt connected, slacken the 
belt. If no relief is afforded by these means, shut 
down, keeping the machine running slowly until the 
shaft is cool, in order that the bearing may not 
“freeze.’’ Renew the oil supply before starting 
again. A new machine should always be run at a 
slow speed for an hour or so in order to see that it 
operates properly. The bearings should be inspected 
at regular intervals to insure that they always remain 
in good condition. The higher the speed, the more 
care should be taken in this regard. 

A warm bearing, or “hot box,” is probably due 
to one of the following causes: 


CARE AND OPERATION 


151 


(a) Excessive belt tension. 

(b) Failure of the oil rings to revolve with the shaft. 

(c) Rough bearing surface. # . 

(d) Improper lining up of bearings or fitting of the journal 

boxes. 

(e) Bent shaft. 

(f) Use of poor grade or dirty oil. 

(g) End thrust, due to improper leveling. A bearing may 

become warm because of excessive pressure exerted by 
the shoulder of the shaft against the side of the bearing. 

(10 Bolts in the bearing cap may be too tight.. 

(i) End thrust, due to magnetic pull, rotating part being 

11 sucked ’ 1 into the field because it extends beyond the 
field poles further at one end than the other. . 

(j) Excessive side pullj because the rotating part is out of 

center. 


Starting Constant-Speed Motors, Shunt or Com¬ 
pound. _(1) Examine the oil level in each bearing 

and see that the oil rings are in good operating con¬ 
dition, Inspect all connections for loose screws or 

wires. 

(2) See that hearings are well supplied with a 
good lubricating oil and that oil rings are free to 

(3) Make sure that the lever arm of the starting 
box or controller is in the “off” position. 

(4) Close the main switch, or circuit breaker. 

(5) Close field switch. ^ .. 

(6) Move lever arm of starting box or control e 
to the running position, pausing long enough on each 
notch to allow the motor to come up to the speed ot 


that notch. , . , . ... „ 

(7) If iisino- a controller, throw the short-circuit! g 

switch and move controller handle back to the start¬ 
ing position. If using a starting box, the lever arm 
should remain in the running position. 


152 


ELECTRIC MOTORS 


To Shut Doum Const ant-Speed Motors. —(1) Open 
the main switch or circuit breaker. 

(2) After the motor has come to rest, see that the 
lever arm of the starting box has returned to its 
original position. 

(3) Open the field switches. 

(4) Clean the machine thoroughly and put in 
order for next run. 

Starting Variable-Speed Motors. — (1) Examine 
shunt field rheostat, and see that all resistance is cut 
out. 

(2) Follow all directions givfen under “Constant- 
Speed Motors. ’’ 

(3) After motor is running on full line voltage, 
gradually cut in resistance in the shunt field rheo¬ 
stat until the motor is up to the desired speed. 

To Shut Down Variable-Speed Motors. —(1) Grad¬ 
ually cut out the resistance in the shunt field rheostat 
until the machine is running on a full field. 

(2) Follow directions given under “To Shut Down 
Constant-Speed Motors.’’ 

Starting Series Motors. —(1) Follow same instruc¬ 
tions as those given for “Starting Constant-Speed 
Motors,” except there is no field switch to close. 

To Shut Down Series Motors. — (1) Open main 
switch or circuit-breaker. 

(2) Examine machine carefully, wipe off all dirt 
or oil, and put in good shape for next run. 

Belts. —The belt on a belt-connected machine should 
be tight enough to run slowly without slipping, but 
the tension should not be too great or the bearings 
will heat. Belts should run with, not against, the 
inside lapping, and the joints should be dressed 


CARE AND OPERATION 


15? 


smooth so that there will he no jarring as it passes 
•over the pulley. 

The crowns of driving and driven pulleys should 
be alike, as “wobbling” of belts is often caused by 
pulleys having unlike crowns. If this is caused by 
bad joints, they should be broken, and cemented over 

again. 

A wave motion or flapping is usually caused by 
slippage between the belt and the pulley, resulting 
from loose belt, grease spots, etc. It may, however, 
be a warning of an excessive overload. This fault may 
sometimes be corrected by increasing the tension, but 
a better remedy is to clean the belt. A back-and- 
forth movement of the pulley is caused by unequal 
stretching of the edges of the belt. If this does not 
cure itself shortly, examine the joints. If they are 
evenly made, and remain so, the belt is bad, and 

should be discarded. 

Static Sparks from Belts .—It sometimes occurs on 
belted machines, especially in dry weather, that 
charges of static electricity accumulate on the belt, 
which may be of sufficiently high potential to cause 
discharges to ground. If the frame of the machine 
is not grounded, these charges may jump to the arma¬ 
ture or field winding, and thence to the ground, punc¬ 
turing the insulation. The belt and frame may be 
discharged by placing a number of sharp metal 
points, which are carefully grounded, close to the 
belt at a point near the motor pulley. If the field 
frame is grounded, there should be no danger to the 

insulation. 

Refusal of Motor to Sfarf.-There are many causes 
for this trouble, among which may be mentioned the 

following: 



154 


ELECTRIC MOTORS 


(a) There may be no current on the line. This can be tested 
at the switch. 

<b) Poor contact of brushes or wrong position of brushes. 
Brushes should be at points diametrically opposite each 
other. 

<c) On series motor there may be an open circuit in armature 
or fields. If the motor is shunt or compound-wound, an 
open circuit in the armature may be the cause. 

(d) If, upon starting, a fuse burns out, it may be caused by: 

(e) Too fast manipulation of the rheostat arm. Usually from 

20 to 30 seconds of time are required for the safe start¬ 
ing of a motor. 

<f) The motor may be stuck fast in some way, or it may 
be overloaded. 

(g) The motor connections may be wrong. 

(h) The field circuit may be open, thus preventing the armature 

from generating the required counter-electromotive force. 

(i) The supply voltage may be higher than the motor was 

designed for. 

(j) There may be a short-circuit in the armature or in the 

field winding. In a two-wire system a short-circuit may 
be caused by two grounds. In a three-wire system with 
grounded neutral, one ground will cause a short-circuit. 

(k) Field density light; due probably to short-circuit of part 

of the coils, or to grounded wires. Indicated by a por¬ 
tion of the field being heated above normal temperature. 

(l) The fuses may be too small to carry the required current, 

or the contacts may be loose, or require cleaning. 

Speed of Motor Too Slow .—Caused by: 

(a) Too great field strength. Fields may have been connected 

in parallel, when designed for series, in which case they 
will run hot. 

(b) Applied e.m.f. too weak, due to long supply line, or too 

small wire in branch circuit connecting with motor. 
These conditions would not affect the motor running 
light, but when a heavy load is thrown on, the speed 
would fall below standard. 

(c) If the motor is of the series type, it may be overloaded. 


CARE AND OPERATION 


155 


Speed of Motor Too High— Caused by: 

(a) Weak field strength, due to short circuit, wrong connec¬ 

tions, improper winding. Part of the field winding may 
be connected in opposition to the other part, as for in¬ 
stance in a compound motor, the series coils may be 
connected so as to oppose the action of the shunt wind¬ 
ing, in which case the speed of the motor will increase as 
the load increases, until if overloaded, the excessive 
armature current due to weak fields will finally cause the 
fuses to blow or perhaps damage the armature wind¬ 
ing. In case the trouble is due to field strength, it 
cannot be remedied by the addition, or the removal of 
wire. The only remedy is a re-winding of the field 
magnets with larger wire if the field is weak, or with 
smaller wire in case there is too great a field strength. 

(b) If the motor is of the series type it will speed up. in 

case of light load. Therefore, a series motor requires 
constant regulation when carrying a variable load. 

Sparking at the Brushes .—Sparking at the brushes 
of compound motors is generally due to improper con¬ 
nection of the field coils; since this type of motor is 
wound with series fields, either opposing or assisting 
the shunt fields. In the case of series or shunt motors, 
sparking at the brushes may be due to any one of 
the following causes: 

(a) Surface of commutator rough; bearing surface of brushes 

worn, jagged or uneven; dirt on commutator. 

(b) Brushes leaving the commutator at intervals, due to 

insufficient tension of the springs which keep the brushes 

in contact with commutator. , 

/ c \ Bearing surface of brushes either too narrow or too wide. 
If too narrow, it will break contact with one commutator 
bar, before coming in proper contact with the next bar. 
If too wide, it may short-circuit several coils, and the 
breaking of this current will cause sparking. 

(d) Brushes may not be correctly spaced. They should be 
diametrically opposite each other, except in some special 
types of machines. 


156 


ELECTRIC MOTORS 


(e) Brushes may not be in the proper position. They should 
be at the neutral point, which is found by slightly shift¬ 
ing the brushes back and forth on the commutator until 
the point of least sparking is found. Variations in 
the load also require a slight change in position of 
brushes to prevent sparking. 

Changing Direction of Rotation .—This is accom¬ 
plished by reversing the connections of either the field 
circuit or the armature. Reversal of both will not 
affect the direction of motion of the armature. 


CHAPTER IX 


ARMATURE WINDINGS FOR ALTERNATING-CURRENT 

MOTORS 

Stationary and Rotating Armatures .—In all direct- 
current motors the field is stationary and the armature 
is the rotating part, while in alternating-current 
motors, the armature may be either the rotating or 
the stationary part, depending upon the type of 
machine and its construction. 

In the case of small synchronous motors, the arma¬ 
ture is usually the rotating part; while in the case 
of large synchronous motors, it is usually the station¬ 
ary part. 

In the case of the commutator types of motors, the 
armature is the revolving part, as in the direct-current 
motors, and the windings are very similar to the 
windings for direct-current motors. 

The winding of the stator of the induction motor 
is practically the same as the armature winding of a 
revolving-field synchronous motor. The rotor of the 
induction motor may be of either the squirrel cage 
or wound type. In the squirrel-cage construction 
there are a number of copper bars imbedded in slots 
in the surface of the armature, and these are all con¬ 
nected together at the ends of the armature by metal 
rings of low resistance. The wound rotor has a 
winding similar to the winding of the stator, and the 
terminals of this winding are brought out to an 

157 


158 


ELECTRIC MOTORS 


external controlling resistance by means of slip rings 
and brushes. 

In general, the windings for alternating-current 
motors are practically the same as the windings for 
the armature of the alternating-current generator, 
and only a few of the types will be discussed in the 
following sections. The reader will have to refer to 
some of the standard books on armature windings 
for a complete discussion of the many different types. 

Comparison of Direct-Current and Alternating- 
Current Armature Windings. — In comparing the 
armature windings of direct-current machines wdth 
those for alternating-current machines, it is evident, 
first of all, that re-entrant or closed coil direct-current 
windings must of necessity be two-circuit or multiple- 
circuit windings, that is, they must have at least two 
paths in parallel through the armature between the 
brushes. On the other hand, the armatures of alter¬ 
nating-current dynamos and synchronous motors may, 
and generally do, from practical considerations, have 
one-circuit windings, that is, windings having one 
circuit per phase. 

With the exception of the A (delta) connected 
polyphase windings, and the short-circuited windings 
of “squirrel-cage” induction motors, both of which 
are of the re-entrant or closed-circuit type, the wind¬ 
ings of alternating-current armatures are essentially 
nonre-entrant or open-circuit windings. 

Classification of Armature Cores. —Armatures for 
alternating-current motors may be classified according 
to the form of the core into three groups, as follows: 

(a) Drum armatures. 

(b) Ring armatures. 

(c) Disk armatures. 


armature; windings 


159 


The ring and disk types are less stable, from a 
mechanical standpoint, than is the drum type. The 
ring armature, other things being equal, requires more 
wire to be wound upon it for a given output than 
does the drum armature and, therefore, has a greater 
inductance than the latter type. Drum armatures 
for alternating-current machines have laminated iron 
cores similar in construction to the armature cores 
for direct-current machines. This applies to alter¬ 
nators of either the revolving or the stationary ai ma¬ 
ture type. 

Armatures for alternating-current motors-may be 
classified according to the construction of the core 
into two groups, as follows: 


(a) Smooth-core armatures. 

(b) Toothed-core armatures. 

(a) In the smooth-core armature, the conductors 
are arranged in flat coils, lie on the surface of the 
core, and, in some cases, the coils are bent down over 
the ends of the core and fastened by end plates or by 
blocks of wood or fiber. In other cases the coils are 
flat or “pancake” shaped and of the same length as 
the armature core, being laid upon the cylindnca 
surface of the core and securely bound with wire 
bands. Smooth-core armatures produce a wave ot 
electromotive force or current that is very nearly har¬ 
monic (sinusoidal) or slightly flat-topped. The induc¬ 
tance of a smooth-core or surface-wound armature 
is much less than that of a toothed-core armature. 

(b) Owing largely to their weak mechanical struc¬ 
ture, smooth-core armatures have been superseded 
in modern practice by the toothed-core type m which 
the conductors are laid in slots, the sides and bottom 


ICO 


ELECTRIC MOTORS 


of which are insulated by mica-canvas, micanite, or 
other suitable insulating material. The conductors, 
which are also insulated, being cotton covered, are 
usually wound into coils on formers, each coil being 
taped and then impregnated with insulating com¬ 
pound or varnish, after which they are baked in ovens 
for the purpose of drying them thoroughly. 

This type of armature is often referred to as an 
iron-clad armature, owing to the fact that when the 
conductors are laid in the slots between the teeth, 
the latter usually project slightly over the conduc¬ 
tors, thus affording a thorough protection and secur¬ 
ing the conductors firmly in place against the action 
of centrifugal force. This construction also serves 
to shield the conductors from the racking action of 
the magnetic drag, due to the magnetic field. 

Types of Armature Conductors .—According to the 
form of conductors used, armature windings for 
alternating-current machines may be divided into 
three classes, as follows: 

(a) Wire winding 

(b) Strap winding 

(c) Bar winding 

(a) Wire winding consists of machine-wound coils, 
formed and insulated before being placed in the slots 
of the armature. This type of winding is usually 
employed in machines having a low current output, 
but working on high potentials. 

(b) Strap winding is made of copper strap, forged 
into the required shape and carefully insulated. It 
is adapted for machines of lower voltage and greater 
current output. Both the wire and the strap wind¬ 
ings may be placed in the slots without any median- 


ARMATURE WINDINGS 


161 


ical bending. This prevents damaging the insulation. 
If the slots are of the partially closed type, these 
windings are slipped in from the end. If the slots 
are what is known as the open type, the coils are 
secured in place by wedges of hard fiber. 

(c) In placing bar windings, the bars, after being 
carefully insulated, are slipped into the slots from one 
end of the armature and the end or cross-connections 
are then bolted and soldered to the bars. The over- 



Figure 78.—Single-Phase Winding, One Slot per Pole. 

hanging tips of toothed slots serve to firmly secure 
the bars in place, thus dispensing with band or bind¬ 
ing wires on the armature core. Bar windings usually 
have one or two bars per slot. 

Single-Phase Windings— Figure 78 shows a com¬ 
mon type of single-phase winding, known as the* con¬ 
centrated type , having one coil to each pair of poles, 
or one slot per pole. The sketch A, at the lower left- 
hand corner of the cut, is a sectional view of a por¬ 
tion of the armature core and shows one of the slots 
containing the conductors which form one side of a 
single armature coil standing opposite to the pole of 
a field magnet. In the diagram, the dark lines en- 



162 


ELECTRIC MOTORS 


closing the sector-shaped figures represent the coils, 
and the lines of lighter shade represent the connec¬ 
tions between the coils. 

The radial parts of the sector-shaped figures repre¬ 
sent the portions of the coils that lie in the slots of 
the armature core, and the curved parts of the sec¬ 
tors represent the portions of the coils that lie at the 
ends of the core. The collecting rings are represented 
by two small dark circles at the center of the cut, 



Figure 79.—Single-Phase Winding, Two Slots per Pole. 


one being shown inside the other for the sake of 
clearness. 

The direction of the current at a given instant of 
time is shown by the arrows. At a given instant, all 
electromotive forces under N poles are in one direc¬ 
tion, and all electromotive forces under S poles are 
in the opposite direction. The explanations here 
given apply also to Figures 79, 80, and 82. In Figure 
79 is shown a single-phase winding, known as the 
distributed type , in which there are two slots per 
pole, all the coils being connected in series. 

A sectional view of a portion of the armature core 
is shown by the small sketch A at the lower left-hand 




ARMATURE WINDINGS 


163 


corner of Figure 79. It will be noted that in this 
case there are two slots standing opposite one pole 
face. The direction of the induced electromotive 
force at a given instant is shown by the arrows. 

Tivo-Phase Windings .—A two-phase winding con¬ 
sists essentially of two independent single-phase wind¬ 
ings on the same armature, each winding being con¬ 
nected to a separate pair of collecting rings, thus 
necessitating the use of four collecting rings. Such 
an arrangement is shown in Figures 80 and 82. 



Figure 80.—Two-Phase Winding, One Slot per Pole per Phase. 


In Figure 80 the four collecting rings are repre¬ 
sented at the center of the diagram by two small dark 
circles, one within the other, and two dotted circles 
surrounding these, it being necessary to so place 
them in order to show the connections. The winding 
shown in Figure 80 is of the concentrated type, that 
is, one slot per pole for each phase, one phase being 
represented by the full lines, while the other phase 
is shown by dotted lines. For the sake of con¬ 
venience the two phases will be designated by A and 
B, phase A in Figure 80 being represented by full 
lines and phase B by dotted lines. 






164 


ELECTRIC MOTORS 


Figure 81 shows the arrangement of the slots for 
a two-phase concentrated winding. The slots marked 
a x , a 2 , a 3 , etc., contain the conductors comprising 
phase A, while the slots marked b lf b 2 , b 3 , etc., contain 
the conductors comprising phase B. The slots de¬ 
signed to carry the A windings are also indicated by 
dark lines, while the B slots are dotted. Phase A 
winding passes along slot a x from the front to the 
back end of the armature core; then from back to 
front in slot a 2 ; then from front to back in slot a 3 ; 
then from back to front in slot a 4 ; and so on, the 



Figure 81.—Two-Phase Drum Armature Core, One Slot per 

Pole per Phase. 

various conductors located in slots a lf a 2f a 3 , etc., being 
joined in series by connectors at the front and back, 
while the two terminals are connected to two collector 
rings, as shown in Figure 80. 

The phase B winding, Figure 81, passes along slot b t 
from the front to the back end of the armature core; 
then from back to front in slot b 2 ; then from front to 
back in slot b 3 ; then from back to front in slot ?> 4 ; 
and so on until all the b slots are occupied by conduc¬ 
tors, which are also joined in series at the back and 
the front by connectors similar to the A winding. 




armature windings 


165 


The terminals of the B winding are then connected 
to two collector rings, these being represented by 

dotted lines in Figure 80. 

Figure 82 shows a two-phase distributed winding, 
there being two slots per pole for each phase. The 



Figure 82.—Two-Phase Winding, Two Slots per Pole per Phase. 

heavy dark lines represent phase A, while phase B 
is indicated by dotted lines. Figure 83 shows an end 
view of a portion of a two-phase armature with its 
A and B windings distributed in two slots per pole. 
The coils belonging to the A winding are of a lightei 



Figure 83.—End View Two-Phase Distributed Winding, Two 
8 Slots per Pole per Phase. 

shade in order to distinguish them from the B 

winding. . . . ,. 

The connections between the coils of the A winding 

are represented in both Figures 82 and 83 by full 
lines, while the dotted lines shown the connections 




166 


ELECTRIC MOTORS 


between the coils of the B winding. A brief study 
of Figures 80, 81, and 82 will enable the student to 
fully comprehend the meaning of the term difference 
in phase, and what causes it. It has already been 
explained that the electromotive force generated in 
an armature conductor reaches its maximum value 
when that conductor is directly under, or in front of, 
a pole face, and is cutting the lines of force at right 
angles to their direction. It has also been explained 
that the conductors carrying phase A are represented 
in Figure 80 and 82 by full lines; and the conductors 
carrying phase B, by dotted lines. 

Comparing Figures 80 and 82 with Figure 81, 
it will be noted that the full line, or A-phase, con¬ 
ductors are carried in slots a ly a 2 , a 3 , a±, etc.; and 
in the position shown, these slots are directly in front 
of the pole faces. Therefore, the value of the electro¬ 
motive force induced in the A-phase conductors is, 
at this particular instant of time, at a maximum; 
while at the same instant the 5-phase conductors, 
represented by the dotted lines and carried in slots 
b i, b 2 , b 3 , b±, etc., are, as shown in Figure 81, midway 
between adjacent poles and moving in a direction 
parallel with, instead of at right angles to, the lines 
of force. Consequently, the value of the electromo¬ 
tive force induced in the B conductors is for the mo¬ 
ment at zero. During the time that a given conductor, 
or a given bunch of conductors, moves from the cen¬ 
ter of a given north pole to the center of the next 
north pole, the electromotive force in the conductor, 
or bunch of conductors, passes through a complete 
cycle of values, that is, from maximum to zero and 
from zero to maximum. 

In the two-phase alternator, the electromotive 


ARMATURE WINDINGS 


167 


forces in the respective windings, as for instance, 
winding A and winding B in Figures 80 and 82, ar¬ 
rive at their maximum values 90 degrees, or one- 
fourth of a period, apart. 

Three-Phase Windings .—A three-phase winding 
consists of three independent single-phase windings 
arranged on the same armature core and having 
their terminals connected to three collecting rings, 
as shown in Figures 86 and 87. This system of wind¬ 
ing may perhaps he better understood if we consider 
for a moment three similar single-phase armatures, 
mounted side by side on the same shaft. These three 
armatures may be designated by A , B, and C. They 
are exact counterparts of each other in every detail, 
each having as many slots as there are field poles, 
and all three armatures are to be revolved in the 
same magnetic field. Let time be reckoned from the 
instant that a given slot of armature A is directly 
under, or in front of, an A-pole face. The time con¬ 
sumed by this armature slot in passing from the 
center of one A-pole face to the center of the next 
A-pole face may be expressed by t. Then the arma¬ 
ture B is to be so mounted on the shaft that its slots 
will be squarely under, or in front of, the pole faces 
at the instant ; while the armature C is to be so 
mounted on the shaft that its slots are directly under, 
or in front of, the pole faces at the instant %t. The 
time t represents a complete cycle, and the three 
electromotive forces generated by the three armatures 
arranged as described will consequently be 120 de¬ 
grees apart in phase. A three-phase alternator is 
simply a combination of three single-phase alterna¬ 
tors, with this exception, that instead of there being 
three separate armatures, the windings are placed 


168 


ELECTRIC MOTORS 


upon a single core having three slots per pole. Fig¬ 
ure 84 shows the arrangement of the slots for such a 
winding. 

The slots designed to carry the phase A winding 
are represented by dark lines marked a lf Ct 9 y 05*3 j CL 
etc. Those designed to carry phase B windings are 
shown by dotted lines marked b lf b 2 , etc., while 
the slots belonging to phase C winding are drawn in 
lightly shaded lines and marked c ly c 2 , c 3 , etc. The 
arrangement of the windings is as follows: The A 



Figure .84.—Three-Phase Drum Armature Core, One Slot per 

Pole per Phase. 

winding passes from the front to the back end of the 
core by way of slot a x ; then from back to front by 
way of slot a 2 ; then from front to back in slot a 3 ; 
then from back to front by way of slot a A ; returning 
to the back by way of slot a 5 , and so on until the 
terminal is finally brought to the front end of the 
armature by way of slot a 8 . The B winding passes 
from front to back in slot b x ; returns to the front in 
slot b 2 ; again passes to the back in slot Z> 3 ; returning 
to the front in slot ; and so on until its terminal 
emerges from slot b 8 . The C winding enters slot c 1 
through which it passes to the back end of the arma- 





' ARMATURE WINDINGS 


169 


ture; returning to the front in slot c 2 ; then from 
front to back by way of c 3 ; returning by way of c 4 ; 
and so in in regular order until its terminal finally 
appears at the front by way of slot c 8 . There being 
one slot per pole for each winding (A, B, and C). 
the winding just described is of the concentrated 

type. 



-Fie-ure 85—End View Three-Phase Distributed Winding. Two 
6 ‘ Slots per Pole per Phase. 



Figure 86—Three-Phase Concentrated Winding, Y Connected. 

Distributed windings are also frequently used for 
three-phase alternators. This style of winding is 
shown in Figure 85, which shows a portion of a three- 
phase armature with its A, B, and C windings each 
distributed in two slots per pole, the coils belonging 
to the respective windings being differently shaded m 
order to distinguish them. Figures 86 and 87 show 
the winding and connections of a three-phase anna- 





170 


ELECTRIC MOTORS 


ture, the winding being of the concentrated type. 
There being three circuits in a three-phase alternator, 
it follows that if they are to be entirely independent, 
six collector rings must be used, two for each wind- 



Figure 87.—Three-Phase Concentrated Winding, A Connected. 

ing; however, the circuits may be kept practically 
independent by using four collector rings and four 
mains, one collector ring being common to all thre^ 
phases. 






CHAPTER X 

COMMERCIAL TYPE OF ALTERNATING-CURRENT 

MOTORS 

General Classifications. —Alternating-current mo¬ 
tors may be divided into three classes, with reference 
to the fundamental principles of operation, as follows: 

(a) Synchronous motors 

(b) Induction motors 

(c) Commutator motors 

In some cases a motor may be a combination of 
two of the above types, as, for example, a single- 
phase induction motor may be so constructed that it 
will start as a repulsion motor when a good starting 
torque is required. 

Alternating-current motors may be divided into 
four classes, with reference to their speed charac¬ 
teristics, as follows: 

(a) Constant-speed motors 

(b) Multi-speed motors 

(c) Variable-speed motors 

(d) Adjustable-speed motors 

(a) The constant-speed alternating-current motor 
is one whose speed does not change at all or a very 
small amount unless there is a change in the fre¬ 
quency of the current being supplied to it. The 
synchronous motor is a good example of this type. 

171 


172 


ELECTRIC MOTORS 


(b) The multi-speed alternating-current motor is 
one that can be operated at several speeds, each speed 
being practically constant for all loads within the 
capacity of the machine. The* induction motor hav¬ 
ing a stator wound so that the number of poles can 
be changed while the motor is in service is a good 
example of this type. 

(c) The variable-speed alternating-current motor 
is one whose speed varies with the load. The series 
alternating-current motor is a good example of this 
type. 

(d) The adjustable-speed alternating-current mo¬ 
tor is one whose speed is practically constant when 
once adjusted, regardless of the load, so long as the 
load does not exceed the capacity of the machine. 

SYNCHRONOUS MOTORS 

Fundamental Principle of the Synchronous Motor. 
—Considered from an electrical and mechanical stand¬ 
point, the synchronous motor is identically the same 
as the alternating-current generator; in fact, the 
same machine is often used as either a generator or 
a motor, according to circumstances and the demands 
of service. The compounding of an alternator, if 
the machine has one, is disconnected when the ma¬ 
chine is operated as a motor. 

Consider for a moment an alternating-current gen¬ 
erator that is being driven by power supplied by a 
small steam engine or an auxiliary motor. When 
a given armature conductor of this generator is di¬ 
rectly under, or in front of, a north magnetic pole 
of the field, the current in the conductor is in such 
a direction that the force which the field exerts on 
the conductor tends to oppose the motion of the 


COMMERCIAL TYPE 


173 


armature. When the same conductor has moved 
sufficiently to be under a south magnetic pole of the 
field, the direction of the current will be reversed, 
and the force produced by the magnetic field will 
still oppose the motion of the armature. The power 
required to drive the armature against these opposing 
forces is the mechanical power of the engine or 
motor driving the generator, which is transformed 
into electrical power and supplied to the circuits con¬ 
nected to the terminals of the machine. The field 
magnets of the alternator are excited by means of 
direct current from a machine called an exciter, 
and their polarity remains constant so long as there 
is no reversal of the direct current in their windings. 

Now, suppose an alternating current be caused to 
flow through the armature winding of the alternator 
by connecting it to some outside source such as a 
second alternator. If the speed of the armature is 
such that a given armature conductor moves from 
the middle of a north pole to the middle of a south 
pole during the time of one alternation or one-half 
cycle of the supplied current; and if the direction 
of the current in the armature conductor is such that 
when the given conductor is under a north magnetic 
pole of the field the force exerted by the magnetic 
field upon the conductor helps, instead of opposing 
the motion of the armature; then the driving engine 
or auxiliary motor may be dispensed with, and the 
armature of the alternator will continue to revolve 
at constant speed, provided the frequency of the sup¬ 
plied alternating current is constant. The revolving 
armature may now be used to deliver mechanical 
power to other machinery; and the machine, which 
was originally an alternator, will now be operating 


174 


ELECTRIC MOTORS 


as a synchronous motor. Synchronous motors may 
be designed to operate on either single-phase or poly¬ 
phase systems, and are called synchronous because 
they always run in synchronism with, that is, at the 
same frequency as, the alternator supplying current 
to them. Direct current is always required for the 
field excitation of the synchronous motor, whether 
single-phase or polyphase. This exciting current is 
sometimes supplied by a direct-current generator 
which may be mounted on the shaft of the motor 
or driven by means of a belt, but in the majority of 
cases the current is taken from an entirely separate 
source. 

Speed of Synchronous Motors .—The speed of the 
synchronous motor cannot change unless the speed 
of the generator that supplies it with current changes; 
but this does not imply that the motor always runs 
at the same speed (r.p.m.) as the generator. The 
speed of the motor and the generator will be the same 
if the motor happens to have the same number of 
poles as the generator. 

Representing the speed of the motor in revolutions 
per minute by S, the frequency of the current sup¬ 
plied to the motor by /, and the number of magnetic 
poles the motor has by p, then the value of the speed 
may be determined by the following equation: 

2x/x 60 
P 

Examples. —1. Determine the speed of an 8-pole synchronous 
motor when it is supplied with current from a 60-cycle 
alternator. 

Solution .—Substituting directly in the above equation gives 


2 X 60 X 60 


900 r.p.m. 


8 




COMMERCIAL TYPE 


175 


2. How many poles should a synchronous motor have in 
order to operate at a speed of 600 revolutions per minute when 
it is supplied with current from a 60-cycle alternator? 

Solution. —Substituting directly in the equation for speed 


gives 


600 = 


2 X 60 X 60 

V 


and then solving this equation for p gives 

600 p = 7200 
p = 12 

Adjustment of the Current in the Armature Wind¬ 
ing of a Synchronous Motor .—The current m the 
armature circuit of a direct-current motor is equal 
to the difference in the values of the impressed volt¬ 
age and the counter-electromotive force divided by 
the resistance of the armature circuit. Any change m 
the value of this current, with a constant impressed 
voltage and constant armature resistance, is produced 
by a change in the counter-electromotive force, due 
to a change in either the field strength or the speed, 
or perhaps both. The speed of a direct-current mo¬ 
tor is always such that the sum of the counter¬ 
electromotive force and the resistance drop is equal 
to the impressed voltage. 

There is a counter-electromotive force induced m 
the armature winding of a synchronous motor, an 
its value, as in the case of the direct-current motor, 
depends upon the speed of the motor and the mag¬ 
netic flux per pole. Since the speed of the synchron¬ 
ous motor is constant, the only means by which the 
value of the counter-electromotive force may be 
changed is to change the magnetic flux per pole by 
changing the exciting current. It all the required 



176 


ELECTRIC MOTORS 


changes in the values of the current in the armature 
winding, due to a change in load, had to be taken 
care of by changing the magnetic flux per pole, the 
operation of the motor would be very unsatisfactory. 
This change in magnetic flux per pole, however, is 
not required, for the required change in the value of 
the current in the armature circuit of a synchronous 
motor—due to a change in load—is produced by a 
change in the phase relation of the impressed voltage 
and the counter-electromotive force. If the load on 
the motor, with a constant field excitation, be in¬ 
creased, the position of the armature—when the cur¬ 
rent is a maximum or passing through zero value— 
lags with respect to the poles of the magnetic field 
and, as a result, the phase relation of the counter¬ 
electromotive force and the impressed voltage will 
change and more current will flow in the armature 
and thus produce the necessary torque to drive the 
increased load, unless the load exceeds the capacity 
of the machine. The current supplied to the arma¬ 
ture winding may be in phase with the impressed 
voltage or it may lead or lag the impressed voltage, 
depending upon the value of the excitation. 

With an increase in load on the motor, the arma¬ 
ture lags more and more with respect to the poles of 
the magnetic field. This increase in lag of the arma¬ 
ture allows more current to flow through the arma¬ 
ture winding; but as the current increases in value, 
its phase relation with respect to the impressed volt¬ 
age is changing, namely, the angle between the arma¬ 
ture current and the impressed voltage increases 
with an increase in the value of the current and, as 
a result of the increase in this angle, there will be a 
decrease in the power factor of the circuit supplying 


COMMERCIAL TYPE 


177 


current to the motor. The power supplied to the 
motor will continue to increase with an increase in 
the lag of the armature as long as the product of 
the power factor and the armature current continues 
to increase; but a point is finally reached where the 
power factor decreases faster than the current in¬ 
creases, and beyond this point the motor will not 
develop ample torque to carry its load. When this 
point is reached, the motor will “break down” and 
stop, for the very simple reason that it is not de¬ 
veloping enough torque to handle its load. 

Hunting of the Synchronous Motor .—When the 
load on a synchronous motor is suddenly increased, 
the result is a momentary change in the speed of 
the revolving part of the machine, thus causing a 
change in the phase relation of the counter-electro¬ 
motive force in the armature winding and the im¬ 
pressed voltage. This change in phase relation be¬ 
tween the counter-electromotive force and the im¬ 
pressed voltage results in an increase in current in 
the armature winding. If the speed of the revolving 
part changes very rapidly, there is liable to be a 
current produced in the armature winding in excess 
of that required to drive the load, which results in 
the revolving part of the machine speeding up and 
causing a decrease in current. The total increase in 
speed may be such as to cause the current to be 
lowered below the value required to carry the load, 
and the speed then starts to decrease, then again 
increase. This action of the synchronous motor is 
called hunting. 

The hunting action of a synchronous motor is 
frequently a source of great annoyance, being gen¬ 
erally accompanied with great variations in the value 


178 


ELECTRIC MOTORS 


of the current and also a rapid rise and fall of the 
voltage between the terminals of the motor. Hunt¬ 
ing is frequently caused by periodic changes in the 
speed of the prime mover operating the generator 
supplying current to the motor, especially in cases 
where gas engines are used. The tendency of the 
motor to hunt is greatest where several synchronous 
motors are operated in parallel on the same mains. 
When a number of synchronous motors are in paral¬ 
lel on the same circuit, very large currents may cir¬ 
culate between the motors and thus cause serious 
disturbances, but this condition can be improved by 
connecting a few induction motors to the circuit, 
thus forming what may be termed a mixed circuit. 

Hunting may be reduced by the use of heavy cop¬ 
per frames or dampers arranged so as to surround 
the pole pieces. This arrangement may be made 
more effective by cutting slots in the faces of the 
pole pieces and placing copper conductors therein. 
The currents induced in these damping devices tend 
to prevent sudden changes in the magnetic field 
and thus increase the tendency toward synchronism. 

Field Excitation and Power Factor .—The current 
supplied to non-synchronous motors, such as the in¬ 
duction motor, is always lagging the impressed volt¬ 
age; while the current supplied to the synchronous 
motor may be made to lead or lag the impressed 
voltage at will. This control of the phase relation 
of the current with respect to the impressed voltage 
is accomplished by varying the strength of the mag¬ 
netic field. The counter-electromotive force induced 
in the armature winding of a synchronous motor may 
be changed by changing the field strength, namely, 
an increase in field strength means an merer 


COMMERCIAL TYPE 


179 


counter-electromotive force, and a decrease in field 
strength means a decrease in the counter-electromo¬ 
tive force. Since the speed of the synchronous motor 
is constant, the counter-electromotive force will vary 
directly as the field strength. 

A clear understanding of the effect of a variation 
in field current upon the value of the power factor 
of an induction motor may be obtained by the use 
of several simple diagrams, as shown in Figures 88, 
89 and 90. The diagram in Figure 88 represents a 
condition when the motor is taking a lagging cur¬ 
rent. The line OE represents the impressed voltage, 



Figure 88_Diagram of Synchronous Motor Taking a Lagging 

Current. 

the line OE c the counter-electromotive force, and the 
line OR the resultant pressure acting in the circuit. 
This resultant pressure produces the current in the 
armature of the motor, which unusually has a rela¬ 
tively high reactance and low resistance and, as a 
result, the current lags the resultant pressure be¬ 
tween 80 and 90 degrees, hut in no case can it be as 
much as 90 degrees. The value of pressures and 
the angles have been so chosen in the diagram in 
Figure 88 that the current I taken by the motor 
lags the impressed voltage by approximately. 30 de¬ 
grees. . . 

The diagram in Figure 89 represents a condition 

of affairs when the power input to the motor is the 
same as in the diagram in Figure 88, but the power 




ELECTRIC MOTORS 


'SO 


factor in this case is unity and in the diagram in 
Figure 88 it is equal to the cosine of 30 degrees. 
The power component of the current in the diagram 
in Figure 89 is the same as in Figure 88, and the 
current makes the same angle with the resultant 
voltage OR as in the diagram in Figure 88. It is 
evident that the field excitation of the machine for 



Figure 89.—Diagram of Synchronous Motor Taking a Current in 

Phase with the Pressure. 

conditions shown in Figure 89 must be greater than 
for conditions shown in Figure 88, in order to in¬ 
crease the value of the counter-electromotive force 
to the required value. 

The diagram in Figure 90 represents a condition 
of affairs when the power input to the motor is the 
same as in the diagrams in Figures 88 and 89; the 



Figure 90.—Diagram of Synchronous Motor Taking a Leading 

Current. 


power factor is equal to the cosine of 30 degrees, the 
same as in the diagram in Figure 88, but the current 
in this case is leading the impressed voltage by the 
same amount it is lagging the impressed voltage in 
the diagram in Figure 88. The counter-electromo¬ 
tive force in the diagram in Figure 90 is greater than 
it is in either of the other two diagrams, in order 
that the motor take the same power. 






COMMERCIAL TYPE 


181 


The field excitation of the motor which gives unity 
power factor for some particular load is called the 
normal excitation of the motor for that load. If the 
excitation be decreased below this value, the current 
supplied to the motor will lag the impressed voltage; 
and if the excitation be increased above this value, 
the current will lead the impressed voltage, as in¬ 
dicated in the diagrams in Figures 88, 89, and 90. 

Synchronous Phase-Modifier .—As shown in the pre¬ 
vious section, the synchronous motor, when overex- 



Figure 91—Combining Two Lagging Currents. 

cited, takes a leading current from the circuit to 
which it is connected. If there are other electrical 
devices connected to the same circuit that the syn¬ 
chronous motor is connected to, and they are taking 
a lagging current from the circuit, then the leading 
current to the synchronous motor and the lagging 
current will combine to form a resultant current 
which will be displaced from the line voltage by a 
smaller angle than if both the currents were leading 
or lagging. This resultant relation can be shown 
by reference to Figures 91 and 92. The diagram 
in Figure 91 represents a condition when the current 
I df taken by an induction motor, lags the impressed 
voltage E by the angle a x ; and the current I s , taken 
by the synchronous motor, also lags the impressed 



182 


ELECTRIC MOTORS 


voltage by the angle a 2 . The resultant current I x is 
a combination of Id and I s and it makes an angle 6 X 
with the impressed voltage E. The power supplied to 
such a combination is given by the following equation: 

P x -E xl x x cos 6 X 

The diagram in Figure 92 corresponds to a con¬ 
dition when the field current of the synchronous mo¬ 
tor has been adjusted so that its armature current 
leads the impressed voltage and the value of the 



Figure 92.—Combining a Leading and Lagging Current. 


current supplied to the induction motor and its 
phase relation with respect to the impressed voltage 
remain the same as in the diagram in Figure 91. The 
resultant current I 2 in this second case makes an 
angle 0 2 with the impressed voltage, and the total 
power supplied to the combination is given by the 
following equation: 

P 2 -E xl 2 x cos e 2 

If the total power supplied to the combination is the 
same in both cases, that is, 

P ! = P 2 

then 

Exl x x cos 0 1 = E xl 2 x cos 0 2 



COMMERCIAL TYPE 


183 


It is apparent from the diagrams that 0 2 is less 
than 0 1 and, hence, the cos0 2 will be greater than 
cos 0 19 and the value of Z 2 will he less than the value 
of I x . The synchronous motor, when used as indicated 
in the diagram in Figure 92, reduces the losses m 
the main circuit by reducing the value of the current 
the line must carry in order to transmit a certain 
power, and also improves the power factor of the 
main circuit, but not of either motor circuit alone. 
When used for the purpose of improving the power 
factor of a circuit, the synchronous motor is called 
a synchronous phase-moclifier, and it may or may not 
he delivering mechanical power when used in this 

way. 

INDUCTION MOTOR 

Rotating Magnetic Field .—Suppose the projecting 
arms or poles on the field frame of a dynamo be di¬ 
vided into three groups and the poles belonging to 
one group marked A x , A 2 , etc., those of another group 
B x , B.„ etc., and those of the third group C 19 C 2 , etc., 
as 1 indicated in Figure 93, which shows the field struc¬ 
ture laid out flat. If a. winding be placed on the poles 
belonging to the different groups, alternate coils be¬ 
ing wound around the cores in opposite directions anc 
each of these windings connected to a source. of 
direct-current, the lower ends of the poles belonging 
to any one group will be magnetized alternately 
north and south. If an alternating current be sent 
through the windings, the polarity of each pole will 
reverse twice during each cycle of the current and 
their strength will be changing in value as the value 
of the current changes. By connecting the t iree 
windings to the different phases of a three-phase 


184 


ELECTRIC MOTORS 


circuit, any three poles that occur in succession 
around the frame will not be magnetized to a maxi¬ 
mum polarity at the same time. The time required 
for the maximum polarity to advance from one pole 



I 

N 

N 

N 

s 

s 

s 

N 

n 

S 

N 

N 

N 

s 

s 

S 

m 

S 

S 

N 

N 

N 

s 

S 

N 

s 

s 

S 

N 

N 

N 

s 

V 

N 

s 

S 

S 

N 

N 

N 

SI 

N 

N 

s 

S 

s 

N 

N 



Figure 94.—Three Currents Displaced in Phase by 120 Degrees. 

to the next is one-third of a half period or one-sixth 
of a period. The maximum polarity passes from 
one pole to another around the magnetic frame, which 
results in what is called a rotating magnetic field. 

Assume that three curves A, B, and C, Figure 94, 
represent the currents in the three different circuits 
about the A, B, and C groups of poles. Starting with 

































































































COMMERCIAL TYPE 


185 


the current in the B winding at a maximum positive 
value and in such a direction through the winding 
that the lower end of the pole marked B 1 is a north 
pole, then the current in the phases A and C are 
negative with respect to the current in the phase B 
at this time, but the windings A and C are so con¬ 
nected that the lower end of the poles marked A x and 
C x are both north poles but of less strength than 
the pole B x . At the same time the lower end of poles 
A,, B 2 , and C 2 will all be south magnetic poles. The 
currents in the different windings do not remain 
constant and, as a result, the strength of the poles 
marked B decrease in value, those marked A increase 
in value, and those marked C decrease in value until 
the current in the C winding reaches zero value, when 
the poles marked C start to increase in value but of 
opposite polarity, etc. At the end of one-sixth of a 
cycle, pole A x is of maximum north polarity and 
poles B x and C 2 are of the same polarity as A lt but 
of less strength. At this time poles A 2 , B 2 , and C x are 
all south poles, as indicated in line II. At the end 
of the next one-sixth of a cycle, the polarity of the 
poles will be as indicated in line III. From an in¬ 
spection of this figure, it is readily seen that the 
magnetic field is moving toward the right. 

In the production of the rotating field for com¬ 
mercial purposes, the windings connected to the va¬ 
rious phases are usually distributed and overlap each 
other instead of being confined to certain definite lo¬ 
calities, as indicated in the upper part of Figure 93. 

Speed of the Rotating Magnetic Feld .—The speed 
at which a magnetic field rotates when it is produced, 
as explained in the previous section, may be de¬ 
termined as follows: Let / represent the frequency 


186 


ELECTRIC MOTORS 


of the supplied current and p the number of mag¬ 
netic poles per phase, and since two magnetic poles 
correspond to one cycle, the time required for one 
revolution of the magnetic field will be equal to 

time per revolution -p^2xf 

and 

number of revolutions per second -2 xf + p 

Example .—If there are 10 magnetic poles in the field struc¬ 
ture of an induction motor, at what speed will the magnetic 
field rotate when the winding is supplied with 25-cycle current? 

Solution .—Substituting in the above equation for speed in 
r.p.s. gives 

r.p.s. = 50 -r- 10 = 5 

and the revolutions per minute (r.p.m.) will be 

r.p.m. = r.p.s. X 60 
or 

5 X 60 = 300 

Fundamental Principle of the Induction Motor .— 
If a hollow metal cylinder be mounted on an axis 
inside of a rotating magnetic field, there will be an 
electromotive force induced in the cylinder, due to 
the relative motion of the magnetic field and the 
cylinder, and this electromotive force will produce a 
current in the cylinder which will react upon the 
magnetic field and thus produce a force tending to 
cause the cylinder to rotate. The path taken by the 
current in the cylinder, due to the induced electro¬ 
motive force, is not very w r ell defined and, as a re¬ 
sult, it will not be very useful in producing a force 
tending to turn the cylinder. This difficulty is over¬ 
come by sloting the cylinder in a direction parallel 
to the axis about which it rotates. 

The magnetic flux between the poles of the rotating 
magnetic field can be greatly increased, with the 


COMMERCIAL TYPE 


187 


same current in the winding, by providing an iron 
core to carry the conductors in which the induced 
current is to flow. 

Construction of the Induction Motor .—There are 
tw r o essential parts in every induction motor and 
these are: 

(a) The stator 

(b) The rotor 



Figure 95.—Stator of Induction Motor, Partly Wound. 

(a) The stator of an induction motor is the sta¬ 
tionary part, and its construction is practically the 
same as that of the armature of a rotating-field alter- 
naior. The stator windings are usually placed in 
slots cut in what is called the stator core, which is 
a laminated structure supported by a cast-iron frame, 
instead of being wound on poles as shown in Figure 
93. The stator core of a small induction motor is 
shown in Figure 95. 


188 


ELECTRIC MOTORS 


(b) The revolving part of the induction motor is 
called the rotor, and induction motors are divided 
into two classes depending upon the construction of 
the rotor. 

(1) Squirrel-cage type 

(2) Slip-ring type 

(1) The squirrel-cage rotor consists of metal bars 

or rods imbedded in slots cut on the surface of a 
# 

cylindrical laminated iron core. The ends of these 



metal bars are connected to copper rings placed at 
each end of the core. The resistance of such a wind¬ 
ing is usually very low because the bars are all con¬ 
nected in parallel. A squirrel-cage rotor is shown in 
Figure 96. 

(2) A slip-ring, or wound, rotor is one provided 
with a winding similar to those on the stator, and 
the terminals of this winding are connected to slip 
rings mounted on the shaft. The rotor winding is 
connected to the external circuit bv means of these 
slip rings, which provides a means of starting and 
controlling the motor by being able to vary the re¬ 
sistance of the rotor circuit. 

The rheostat, by means of which the resistance of 











COMMERCIAL TYPE 


189 


the rotor circuit is varied, is sometimes placed in 
the rotor structure of small motors, which does away 
with the necessity of the slip rings, the resistance 
being cut in or out of circuit by means of a rod 
which projects through the hollow shaft. 

Operation of the Induction Motor .—In the opera¬ 
tion of the induction motor there is both a generator 
and a motor action. 

(a) Generator Action.—The flux of the rotating 
magnetic field produced by the current in the stator 
windings cuts across the conductors on the surface 
of the rotor and induces in them an electromotive 
force, which causes a current to flow in the rotor 
circuit. 

(b) Motor Action.—The current produced in the 
conductors on the rotor and the rotating magnetic 
field react upon each other and produce a torque, 
the direction of which is the same as the direction 
in which the magnetic field revolves. 

Speed of the Induction Motor .—Assuming the rotor 
of an induction motor were to revolve at the same 
speed as the rotating magnetic field produced by 
the current in its stator, there would be no relative 
movement of the conductors on the rotor and the 
magnetic field, hence, there would be no induced 
electromotive force in the conductors on the rotor 
and, as a result, there would be'no current in the 
rotor winding. It is apparent that the rotor could 
never run at the same speed as the rotating field, 
unless it was driven from some outside source of 
power, as there would be no torque produced on 
account of there being no current in the rotor wind¬ 
ings. In order that there be a current in the rotor 
winding there must be an induced electromotive force 


190 


ELECTRIC MOTORS 


and, hence, the speed of the rotor must be less (in 
the case of a motor) than that of the magnetic field. 
With a decrease in speed of the rotor, there is an 
increase in rotor current and, hence, an increase 
in torque. The speed of the motor will become con¬ 
stant when the developed torque is just sufficient to 
drive the load, unless the load exceeds the capacity of 
the motor. As the load changes, there will be a 
change in the torque the motor must develop and, 
hence, there must be a change in rotor current which 
is produced by a change in speed of the rotor, result¬ 
ing in a change in the value of the induced electro¬ 
motive force in the rotor. If the load increases, the 
speed will decrease; and if the load decreases, the 
speed will increase. 

Slip of the Rotor .—The difference in the speed of 
the rotating magnetic field and that of the rotor is 
called the slip of the rotor. The slip is approxi¬ 
mately proportional to the load for all loads within 
the range of the normal capacity of the motor. Rep¬ 
resenting the speed of the magnetic field by S , and 
the speed of the rotor by S 1 , then the slip of the rotor 
in per cent, may be computed by means of the fol¬ 
lowing equation: 

Of _ Cfl 

per cent slip = * - x 100 

The slip of the rotor of an induction motor may 
be easily measured, unless it becomes excessive, by 
what is called the stroboscopic method. Mark as 
many equally-spaced radial lines on the end of the 
shaft as there are poles on the motor and illuminate 
these lines by means of an arc lamp connected to 
the circuit supplying current to the stator of the 



COMMERCIAL TYPE 


191 


motor. When the motor is in operation, the radial 
lines appear to rotate in a direction opposite to the 
direction in which the rotor is rotating, and the 
speed of this apparent rotation is proportional to 
the slip of the rotor. 

The light from the arc lamp pulsates in value, and 
if the rotor was revolving at synchronous speed, the 
radial lines would advance the angular distance of 
one pole pitch for each pulsation of the light, and 
the lines would appear to stand still. The speed of 
the rotor is less than the speed of the magnetic field 
and, as a result, the angular advance of the lines i^ 
less than the angular distance of one pole pitch, and 
successive pulsation of the light shows the lines in 
a position slightly behind that which they occupied 
at the previous pulsation. The per cent slip may be 
determined as follows: Let / represent the frequency 
of the current supplied to the motor and t the rate 
at which the radial lines drop back per minute, then 


per cent slip = 


t 

/ x 60x2 


xlOO 


Example .—A 4-pole induction motor is operated on a 60- 
cycle circuit. In determining the slip by the stroboscopic 
method, the radial lines in the end of the shaft dropped back 
at the rate of 108 in one minute. What was the slip in per 
cent? 

Solution .—Substituting in the above equation gives 


per cent slip = 


108 

60 X 60 X 2 


X 100 = 1.5 


Torque of the Induction Motor .—From the discus¬ 
sion of the induction motor in the previous sections^ 
it might be supposed that the maximum torque would 
be produced at zero speed, since the induced electro- 




192 


ELECTRIC MOTORS 


motive force in the rotor, and hence the rotor cur¬ 
rent, is then a maximum. The frequency of the in¬ 
duced current in the rotor is directly proportional 
to the slip of the rotor, and the rotor current lags 
behind the induced electromotive force more and 
more as the slip increases, due to the increase in 
reactance of the rotor circuit. The lagging current 
tends to set up a flux which is opposed to that pro¬ 
duced by the current in the stator windings, and, 
when the slip becomes large, this demagnetizing ac- 



Figure 97.—Speed-Torque Curve of Induction Motor. 


tion is excessive, and the magnetic flux decreases 
more rapidly than the rotor current increases. As 
a result of the demagnetizing effect of the rotor cur¬ 
rent, the speed-torque curve of an induction motor 
is not a straight line but has the general shape, when 
the resistance of the rotor remains constant, shown 
in Figure 97. The ordinate A represents the maxi¬ 
mum torque, and the ordinate B corresponds to syn¬ 
chronous speed or zero torque. 

The torque for lower speeds may be increased by 
increasing the resistance of the rotor circuit, which 
results in a smaller phase displacement of the rotor 
current and the induced electromotive force pro- 






COMMERCIAL TYPE 


193 


during it; hence, a smaller demagnetizing action and 
a greater torque. 

Induction Generator .— An induction motor when 
operating without load takes a very small current 
from the circuit to which it is connected, and the 
speed of its rotor is very near that of the magnetic 
field. If the rotor be connected to some source of 
power and its speed adjusted to correspond to that of 
the magnetic field, the electrical power input to the 
stator will be very small, it being equal to the iron 
loss in the stator. By increasing the speed of the 
rotor or rotating it above synchronism, the stator will 
deliver power to the circuit to which it is connected, 
provided an alternating-current generator is con¬ 
nected to this circuit to fix the frequency. When an 
induction motor is used in this manner, it is called 
an induction generator. Generators of this type are 
very uncommon. 

Induction Motor as a Frequency Changer. —An in¬ 
duction motor provided with a rotor having a wind¬ 
ing with terminals connected to collector rings may 
be used as a frequency changer, that is, it may be 
used to change the frequency. When the rotor of 
an induction motor is held stationary, the magnetic 
flux produced by the current in the stator induces 
electromotive forces in the windings on the rotor that 
are of the same frequency as the electromotive forces 
applied to the stator. If the rotor is run at one-half 
speed in the direction the magnetic field rotates, the 
frequency of the induced electromotive forces in the 
rotor windings wall be one-half the frequency of the 
electromotive forces applied to the stator. By driv¬ 
ing the rotor in the opposite direction to the direction 
in which the magnetic field rotates, the frequency of 


194 


ELECTRIC MOTORS 


the electromotive forces in the rotor windings is 
greater than the frequency of the electromotive forces 
applied to the stator. Thus, if the rotor be revolved 
at one and one-third synchronous speed, the rotor 
electromotive forces will have a frequency one and 
one-third times as great as the stator electromotive 
forces. 

The speed of the rotor, when the induction motor is 
used as a generator, is determined by the speed of the 
prime mover. 

COMMUTATOR MOTORS 

Action of the Direct-Current Shunt Motor When 
Supplied with Alternating Current .—If a direct- 
current shunt motor be connected to an alternating- 
current circuit, the current in the armature and field 
circuits will not be in phase, due to the difference in 
the relation of the resistance and the reactance for 
the two circuits. The armature circuit has a much 
lower reactance in proportion to its resistance than 
the field circuit and, as a result, the field and arma¬ 
ture currents will be displaced from the impressed 
voltage. The magnetic flux per pole lags the field 
current and, hence, the angle between the armature 
current and the field flux is greater than the angle 
between the armature and field currents. 

Since the armature current and field flux are not 
in phase, and since their signs do not change at the 
same time, the torque acting on the armature—which 
is proportional to the product of the armature and 
the field flux—will not be constant in direction dur¬ 
ing the entire cycle. The net torque producing, or 
tending to produce, rotation is the algebraic sum of 
the average torques acting in opposite directions dur- 


COMMERCIAL TYPE 


195 


ing one complete cycle. When the armature current 
and the field flux are displaced in phase by 90 de¬ 
grees, the sum of the torques for one cycle is zero 
and there is no resultant tendency for the armature 
to rotate. 

The torque of the shunt motor can be improved by 
connecting the armature to one phase and the field 
winding to another phase of a two-phase system. This 
method is not satisfactory for commercial purposes, 
due to complications involved in its operation, low 
power factor of the field circuit, and principally be¬ 
cause more satisfactory equipment is on the market. 



Figure 98.—Short-Circuited Coil. 


Commutation is a great deal more complicated 
when the continuous-current motor is used on an 
alternating-current circuit. This can be shown by 
reference to Figure 98, which shows one of the coils 
on the armature short-circuited. When the current 
in the field winding changes in value, there is a 
change in the magnetic flux through the short-cir¬ 
cuited coil and it acts as the short-circuited secondary 
of a transformer and may carry a current many 
times the normal current in the coil. This large cur¬ 
rent causes excessive heating of the armature and 
very destructive sparking when the commutator seg¬ 
ments move from contact with the brushes. 

Action of the Direct-Current Series Motor When 
Supplied with Alternating Current. —If a direct-cur- 




196 


ELECTRIC MOTORS 


rent series motor be connected to an alternating-cur¬ 
rent circuit, the current in the armature and field 
windings will be in phase, since they are in series; 
but the magnetic flux produced by the field current 
and the armature current will not be in phase with 
each other on account of the inductance of the field 
winding. The inductance of the field winding of the 
series motor, however, is much less than the induct¬ 
ance of the field winding of the shunt motor and, 
as a result, the field flux and armature current are 
not displaced in phase nearly so much as in the 
case of the shunt motor, but the commutating diffi¬ 
culties are practically the same. 

Methods of Improving the Commutation of the 
Series Alternating-Current Motor. —Some of the more 
important methods employed in improving the com¬ 
mutation of a series alternating-current motor are as 
follows: 

(a) Reducing the number of turns in each armature coil. 

(b) Reducing the frequency of the circuit to which the motor 

is connected. 

(c) Reducing the flux density in the magnetic circuit. 

(d) Special devices. 

(a) By reducing the number of turns in each 
armature coil, the electromotive force produced in 
the coil is reduced and, hence, the difficulties encoun¬ 
tered during commutation are reduced. If the im¬ 
pedance of the short-circuited coils is reduced in the 
same ratio as the number of turns, there would be 
no improvement in commutation; but such is not 
the case, as the resistance is not reduced directly as 
the turns on account of the resistance of the con¬ 
necting leads, brushes themselves, brush contacts, 
and commutator bars. There will be a larger number 


COMMERCIAL TYPE 


197 


of segments in the commutator of an alternating- 
current series motor than in the commutator of a 
direct-current series motor. 

(b) The electromotive force induced in a short- 
circuited coil depends upon the frequency, and low 
frequences tend to reduce commutation difficulties. 

(c) The electromotive force induced in the short- 
circuited coil, for a given frequency, varies with the 
flux through the coil or the flux density, and commu¬ 



tation difficulties are less with low densities than with 
high. 

(d) The above features in the design and opera¬ 
tion of a series alternating-current motor improve 
commutation, but certain special devices have been 
found necessary in order to make commutation a prac¬ 
tical success. Two of these methods are 

(1) Resistance leads 

(2) Balanced choke coils 

(1) By connecting resistances as indicated in Fig¬ 
ure 99, the local current in a short-circuited portion 
of the armature winding is reduced, since it must 
flow through a part of the armature winding and two 
of the resistances. These resistances are also in 
series with the external circuit and, apparently, de- 












198 


ELECTRIC MOTORS 


crease the efficiency of the machine by increasing the 
resistance losses, but it has been proven experiment¬ 
ally that there is an increase in efficiency as the loss 
due to the load current passing through the added 
resistances is less than the decrease in loss due to the 
smaller current flowing through the short-circuited 
parts. 

(2) The connections of the choke coils are shown 
diagrammatically in Figure 100. The windings of 
these coils are so connected that their inductance is 



Figure 100.—Balanced Choke Coils. 


cumulative in the short-circuited path, but differential 
to the external circuit. This combination is not alto¬ 
gether satisfactory as there is a balance for the ex¬ 
ternal current only when the current is equally di¬ 
vided between the two windings. 

Compensating Windings .—The armature reaction 
in an alternating-current motor and also the in¬ 
ductance of the armature winding may be greatly 
reduced by means of what is called a compensating 
winding. This compensating winding is a distributed 
winding imbedded in slots cut in the pole faces and 
supplied with current by either of the following 
methods. 

(a) Current supplied inductively. 

(b) Current supplied conductively. 








































COMMERCIAL TYPE 


m 


(a) When the compensating winding is short- 
circuited upon itself, there will be a current induced 
in it from the armature by transformer action, and 
the magnetic fields of the two windings tend to neu¬ 
tralize each other. A diagrammatic scheme of con¬ 
nections is shown in Figure 101. 

(b) When the compensating winding is connected 
in series with the armature winding, and the same 
current flows through both, the motor is said to be 
conductively compensated. If the compensating has 




Figure 101.—Connection for Inductive Compensation. Pig. 102. 

Connection for Conductive Compensation. 

the proper number of turns and the current is in the 
proper direction, the magnetic fields of the two wind¬ 
ings tend to neutralize each other. A diagrammatic 
scheme of connections is shown in Figure 102. 

Repulsion Motor .—If a direct-current armature be 
placed in a magnetic field produced by an alternating 
current, as indicated in Figure 103, there will be a 
transformer action taking place, the field winding 
acting as the primary and the armature winding as 
the secondary of the transformer. There will be a 
current between the short-circuited brushes for any 
position of the brushes on the commutator except the 
one shown in the figure. For the position of the 
brushes shown in the figure, the algebraic sum of the 






















200 


ELECTRIC MOTORS 


electromotive forces induced in the coils in either of 
the circuits between the brushes is zero. 

If the brushes be placed in the position shown in 
Figure 104, there will be a maximum current flowing 



Figure 103.—Position of Short-Circuit Brushes for Zero Current. 

between them. The magnetizing effect of this current 
in the armature is opposite to that of the current in 
the field windings and, as a result, the magnetic effect 
of the field windings is partly neutralized. When 


Figure 104.—Position of Short-Circuited Brushes for Maximum 

Current. 

the brushes are in the position shown in Figure 103, 
there will be no resultant torque tending to produce 
rotation of the armature, as one-half of the inductors 
in each of the paths tend to produce rotation in one 














COMMERCIAL TYPE 


201 


direction and the remaining one-half tend to produce 
rotation in the opposite direction. 

If the brushes be moved from the position shown in 
Figure 103, there is no longer zero resultant torque 
acting on the armature. The direction of rotation 
will depend upon the direction in which the brushes 
are moved with reference to the position shown in 
Figure 103. A motor operated in the above manner 
constitutes what is called a repulsion motor. 



Figure 105.—Compensated Repulsion Motor. 


Compensated Repulsion Motor .—The compensated 
repulsion motor is a series alternating-current motor 
with the addition of short-circuited brushes placed at 
right angles to the main brushes, as shown in Figure 
105. The speed characteristic of this type of motor 
and its operation are quite different than either the 
series or the repulsion motor. 

The magnetic effect of the current, due to the short- 
circuited brushes, counteracts to a great extent the 
magnetic effect of the main field winding. This cur¬ 
rent is produced by transformer action as in the 
repulsion motor when the brushes are in the position 
indicated in Figure 104. 

The magnetic effect of the current between the 





















202 


ELECTRIC MOTORS 


main brushes is at right angles to the main field or 
a line joining the short-circuited brushes, as shown 
in Figure 105. The current through the armature 
inductors, due to the short-circuited brushes reacting 
with the magnet flux produced by the main current, 
produces the larger part of the torque of the motor. 
Some torque, however, is doubtless produced by a 
reaction between the flux produced by the series field 
current and the current in the armature inductors 
between the main brushes. With an increase in speed, 
there is an increase in counter-electromotive force in 

IV 

MS 
B 

Figure 106.—Arrangement of Conductors in Slots of Wagner 

“BK” Motor. 

the inductors, and the current between the short- 
circuited brushes becomes less and, hence, the torque 
is decreased. The speed characteristics of this motor 
are very similar to the direct-current shunt motor. 

Combined Compensated Repulsion and Single-Phase 
Induction Motor .—One of the leading manufacturers 
of electrical machinery is making an alternating- 
current motor which is a combination of the compen¬ 
sated repulsion motor and the single-phase induction 
motor. The armature of this motor has two windings, 
a squirrel-cage and a commutated winding. The 
arrangement of these windings in one of the slots is 
shown in Figure 106. The electrical connections are 
indicated in Figure 107. There are currents produced 
in the commutated windings by transformer action 













COMMERCIAL TYPE 


205 


and these currents flow between the short-circuited 
brushes 5 and 6. Currents are also inducted in the 
squirrel-cage winding. The current flowing between 
the main brushes of the commutated winding sets up 
a magnetic flux at right angles to that produced by 
the current in the winding 1. The currents in the 
commutated winding between the short-circuited 
brushes and the current in the squirrel-cage windings 



Figure 107.—Wiring Diagram of Wagner “BK" Motor. 

react with this flux produced by the current between 
the main brushes and thus is produced a torque which 
starts the motor. With an increase in speed, there 
will be a magnetic flux produced by the current in 
the squirrel cage winding in quadrature with the cur¬ 
rent, and it develops a corresponding torque. The 
torque, due to the current between the short-circuited 
brushes, decreases with an increase in speed; and the 
torque, due to the current in the squirrel-cage wind¬ 
ing, increases as synchronism is approached, as in the 
ordinary induction motor. 













CHAPTER XI 


METHODS OF STARTING, SPEED CONTROL, AND OPER¬ 
ATING CHARACTERISTICS OF ALTERNATING- 
CURRENT MOTORS 

Methods of Starting Synchronous Motors. —If a 
single-phase alternator be electrically connected to 
alternating-current supply mains, the machine will 
not start up and run as a motor, unless it be first 
started and brought up to full speed by an engine, or 
other sources of power. This is due to the fact that 
the current in the armature of the machine is rapidly 
reversing in its direction, thus tending to turn the 
armature first in one direction and then in the other 
direction in rapid succession. Therefore, in the case 
of the single-phase synchronous motor, it is necessary 
that the power for starting it be supplied from a 
source independent of the single-phase supply, and 
that the motor be brought up to nearly the exact 
speed of synchronism with its alternator before it can 
be left to run on the current supplied to it. 

Self-Starting of Polyphase Synchronous Motors .— 
On the other hand, if a polyphase alternator be con¬ 
nected to polyphase supply mains, the machine will 
start on this current and run up to full speed, pro¬ 
vided it has little or no load. This self-starting fea¬ 
ture of the polyphase machine is explained as follows: 

The field circuit is to be left open while starting in 
this manner; only the armature is to be connected 
to the polyphase supply. As one of the phases of the 

204 


STARTING, SPEED CONTROL, OPERATION 


205 


current passing through the armature dies away, it 
leaves a small amount of residual magnetism in the 
field-magnet structure, thus creating a rotating field 
such as is produced in the stator winding of an induc¬ 
tion motor. This residual magnetism and rotating 
field act upon the growing current of the other phase, 
or phases,, and produce a small starting torque, which 
will increase to a limited extent, especially if there is 
large armature reactance, which will be the case if a 
concentrated winding is used on the armature. The 
starting torque of the motor will also be greater when 
the motor is provided with a small air gap, than it will 
be if the air gap is large. A polyphase synchronous 
motor started in this way and running on open field 
circuit acts on the principle of an induction motor, 
and its speed gradually increases. When the speed is 
almost up to the speed of synchronism, the field switch 
may be closed, and if the motor now falls into step, 
the load may be thrown on. 

The polyphase synchronous motor, when started 
in the manner just described, develops but little start¬ 
ing effort, the torque being barely sufficient to work 
it up to full speed with no load; therefore, it is gen¬ 
erally started by means of an induction motor or a 
small engine. The larger sizes of polyphase synchro¬ 
nous motors are generally equipped with some such 
starting device, and when the motor is up to speed, 
and thrown into circuit, the load is gradually ap¬ 
plied by means of a friction clutch. The smaller 
sizes are usually self-starting without load, the load 
being applied after the motor has reached synchro¬ 
nous speed. 

This method of starting is objectionable, mainly 
because the machine takes excessively large lagging 


208 


ELECTRIC MOTORS 


currents at starting. This is liable to cause a drop in 
the supply voltage great enough to seriously disturb* 
the general system of distributing mains from which 
the synchronous motor receives its supply current. If 
the motor is of such capacity as to require a large pro¬ 
portion of the generator output, or if the motor is 
used in connection with a lighting service, then the 
excessive demand for current at starting is especially 
objectionable. 

Another serious objection to the self-starting of 
polyphase synchronous motors is the production of 
high voltages in the field coils, due to the fact that, at 
the time of starting, the armature and field windings 
of the motor are related to §ach other as are the pri¬ 
mary and the secondary of an alternating-current 
transformer. The result is that when the field coils 
have many turns of wire, a dangerously high electro¬ 
motive force may be induced in them and there is 
a liability of breaking down the insulation of the field 
coils. This may be avoided by using a few turns of 
large wire in the field winding, thus necessitating the 
use of a low voltage exciter. In this way, exciters 
giving electromotive force as low as 50 volts may be, 
and are frequently, used. 

Another method is to provide short-circuited metal 
rings around the field poles. These rings limit the 
changes of magnetism in the pole pieces, and thereby 
prevent the formation of excessively high induced 
voltages in the field coils. 

Starting Compensator .—This device, for a two- 
phase synchronous motor, consists of two transform¬ 
ers ; and for a three-phase machine, three transform¬ 
ers are used. The transformers have their primaries 
connected across the respective phases of the supply 


STARTING, SPEED CONTROL, OPERATION 207 

mains, while their secondaries are provided with a 
number of taps so that, at starting, a fraction of the 
full supply voltage can be applied to the armature 
terminals of the motor. This fraction is usually from 
40 to 60 per cent of the full voltage. A switching 



Figure 108.—Interior View of Floor Type Starting Compensator. 

device is provided by means of which the change from 
fractional to full voltage can be quickly made when 

the motor reaches full speed. 

In construction and operation the starting com¬ 
pensator resembles an auto transformer. Figure 108 
shows an interior view of the starting compensator 
built by tho Fort Wavne Electric Company, and may 











203 


ELECTRIC MOTORS 


be described as follows: An inductive winding, pro¬ 
vided for each phase, is mounted on a separate leg 
of a branched magnetic core made up of laminated 
iron stampings. These windings and core, together 
with a cable clamp and switching mechanism, are 



Figure 109.—Interior View of Wall Type Starting Compensator. 


assembled in a ease with external operating handle 
and release lever. 

These compensators are built in six sizes, the first 
four sizes being the wall suspension type, and the re¬ 
maining sizes the floor type shown in Figure 108. The 
wall type, an interior view of which is shown in 
















STARTING, SPEED CONTROL, OPERATION 209 

Figure 109, is made up in the following sizes: 60 
cycle—5 to 200 horsepower; 40 cycle—5 to 135 horse¬ 
power ; 25 cycle—5 to 100 horsepower. The larger 
capacities are built in the floor type, shown in Fig¬ 
ure 108. 

Each compensator is assembled in a metal case that 
is dust proof under ordinary conditions. In both 
types the covers may be readily removed for inspection 
of the interior or for changing the connections to alter 
the ratio of transformation. In the wall type com¬ 
pensator, the switch is located at the bottom, and the 
oil tank enclosing the switch may be removed sepa¬ 
rately for inspection, renewal of oil or contacts, etc., 
without taking the compensator down from the wall 
or disconnecting any of the leads. In the floor type, 
the switch is located in the upper part of the com¬ 
pensator casing and is equally accessible. 

Windings of Compensators .—The inductive wind¬ 
ings mentioned above are given a very thorough in¬ 
sulating treatment after being placed on the laminated 
core. They are placed in a large tank and baked under 
a high vacuum until every particle of moisture is 
driven out. An insulating compound is then intro¬ 
duced into the tank in a molten condition and forced 
into the coils under high pressure. This penetrating 
treatment fills every minute pore and, on solidifying, 
seals them in such a manner that it is absolutely im¬ 
possible for moisture to enter. Besides making the 
windings moisture proof, this process gives a much 
greater mechanical stability to the coils. 

Several taps are brought out from each coil, so that 
by connecting to the proper tap, the required starting 
current may be obtained to best suit each require¬ 
ment. The particular tap is determined by trial at 


210 


ELECTRIC MOTORS 


the time of installation and the connections made 
permanent. 

These taps provide for starting the motor at 80, 
65, and 50 per cent of the line voltage with corre¬ 
sponding line currents of 65, 42, and 25 per cent of 
the current that would be taken by the motor if it 
were started direct from the mains. For larger mo¬ 
tors, taps are provided to give a starting potential of 
85, 70, 58, and 40 per cent of the line voltage, giving 



Figure 110.—Connections of Three-Phase Starting Compensator 

with No-Voltage Release. 


respective currents equal to 72, 40, 34, and 16 per 
cent of the current that would be taken by the motor 
if no compensator were used. The three coils of the 
three phases are connected in Y, the line to the three 
free ends of the coil, and the starting connections of 
the motor to the taps, as shown in Figure 110. 

In two-phase compensators, the line is connected 
to the ends of each coil, and the starting connections 
of the motors to the taps and the other ends. 

The double-throw oil switch, provided with heavy 
wiping contacts within the compensator, is operated 
by a lever on the right of the case. The shaft of the 





























































STARTING, SPEED CONTROL, OPERATION 


211 


switch, to which the operating lever is attached, also 
extends through the case to the left, where a trigger 
holds it in the running position, Figure 108. 

The starting lever has three positions: Off, Starting , 
and Running. In the off position, the lever stands 
vertically, with no connection existing between the 
motor and the line. Thus the compensator switch 
takes the place of the main line switch. In the start¬ 
ing position the line is connected to the terminals, and 
the motor to the taps of the compensator winding. In 
the running position, the compensator winding is cut 
out, and the motor is connected to the line fuses, or 
overload relays mounted above the compensator. 

An automatic latch is arranged so that from off 
the lever can he thrown backward into the starting 
position; and thence forward into the running posi¬ 
tion only by a quick throw of the lever. This arrange¬ 
ment prevents the attendant from throwing the motor 
directly on the line, thereby causing a rush of cur¬ 
rent which it is the object of the compensator to avoid, 
and also eliminates any appreciable drop in speed, and 
consequent increase in current passing from the start¬ 
ing into the running position. 

The compensators are designed for one-minute 
starting duty, and a tap should be chosen which will 
not give so low a voltage as to require over one minute 
for starting. This precaution is necessary to pre¬ 
vent over-heating, which is liable to happen to any 
starting device if carelessty handled. A strong spring 
prevents the swatch from being left in the starting 
position. 

The external lever is held in the running position 
until released either by hand or by the action of a 
no-voltage relay. This protective device consists of 


212 


ELECTRIC MOTORS 


a cast-iron frame, open at the bottom and totally 
enclosing the coil, so that it is neither exposed to 
damage in handling nor affected by foreign substances. 
A fiber piece covers the opening through which a lami¬ 
nated plunger connects with the tripping lever; this 
lever engages with the trigger on the switch shaft. 
Figures 110 to 113 show the connections of com- 



Figure 111.—Connections of Two-Phase Starting Compensator 

with No-Voltage Release. 


pensators furnished with no-voltage release. Connec¬ 
tions for the series-relay attachment are shown in 
Figures 112 and 113. 

The overload relays are arranged to open the no¬ 
voltage relay circuit, allowing the laminated core to 
drop, and thereby releasing the switch. When prop¬ 
erly adjusted, these relays have the advantage of pro¬ 
tecting the motor against running single-phase, the 
increased load caused by the motor running single- 
phase being sufficient to trip the relay. 



















































































STARTING, SPEED CONTROL, OPERATION 213 : 

Relays furnished with compensators for 1040- to 
2500-volt circuits are wound for 110 volts and conse¬ 
quently should be connected to some low tension cir¬ 
cuit which would he affected in case of the failure of 
the voltage of the motor, or through a small trans¬ 
former to the motor leads. 



In synchronous motors of the stationary field type, 
the field circuit may be broken up into many separate 
parts and brought out to convenient switches located 
on the front of the machine so as to divide up the 
induced electromotive force. While Parting the mo¬ 
tor, these switches are left open; and when the ma¬ 
chine has reached synchronous speed, these switches 
are closed, thus connecting all the field coils m series 

with the exciter. 

Speed Control of Synchronous Motors. The speed 
of a synchronous motor, when it is operated on a cir- 














































































2 14 


ELECTRIC MOTORS 


cuit of constant frequency, is constant. If the load 
the motor is operating exceeds the capacity of the 
motor, the motor will stop, or break down, as it is 
called in practice, instead of merely decreasing in 
speed. The speed of a synchronous motor may be 



changed by changing the frequency of the supplied 
current, but this is little used. 

Phase Characteristics of the Synchronous Motor .— 
The current required to operate a synchronous motor 
w T hen it is driving a certain load, and the phase rela¬ 
tion of this current and the impressed voltage, will 
depend upon the excitation of the motor. The phase 
characteristic of a synchronous motor is a curve show- 
























































































STARTING, SPEED CONTROL, OPERATION 


215 


ing the relation between the armature current and 
the field excitation, the test being made under con¬ 
stant conditions with respect to voltage, frequency, 
and load. Phase characteristics are shown in Figure 
114. Curve A corresponds to full load, curve B to 
one-half load, and curve C to light load. 

Starting Single-Phase Induction Motors. —An in¬ 
duction motor designed to operate on single-phase 
current is called a single-phase induction motor, but it 



Figure 114.—Phase Characteristics of the Synchronous* Motor. 


will not start unless provided with some sort of a 
special starting arrangement. Pour methods arei m 
general use for starting single-phase motors, ihej 

are as follows: 


(a) Hand starting 

(b) Split-phase starting 

(c) 11 Shading-coil ’ 9 starting 

(d) Repulsion motor starting 

(a) Hand Starting. — Very small single-phase in¬ 
duction motors may be started by a vigorous pull 
on the belt connecting the motor to the driven 

“Tb ^SpUt-Phase Starting .-By means of the proper 
arrangement of wiring, a single-phase alternating cur- 





J216 


ELECTRIC MOTORb 


rent can be split into two parts and used exactly 
as a two-phase current is used. This is accomplished 
by allowing the single-phase current to divide itself 
between two branches of an auxiliary circuit in which 
the ratio of resistance to reactance is different in the 
two branches. This de-phasing of the two parts of a 
single-phase alternating current is called phase split¬ 
ting, and, by taking advantage of this peculiarity of 
the alternating current, it is possible to obtain from 
a single-phase alternating current a two-phase current 
which can be utilized for starting a single-phase in¬ 
duction motor, provided the motor be arranged so as 
to start as a two-phase motor; and when the rotor 
has attained full speed, the auxiliary, or starting 
circuit, can be cut out of service, after which the 
motor continues to run at full rated speed on the sin¬ 
gle-phase current. Various methods and devices are 
in use by manufacturers of induction motors for ac¬ 
complishing this result. In the single-phase induction 
motor built by the Holtzer-Cabot Electric Company, 
one set of stator coils, termed the working coils, con¬ 
sists of many turns of coarse wire, occupying three- 
fourths of all the stator slots; while the other set of 
stator coils, termed the starting coils, consists of fewer 
turns of fine wire, occupying one-fourth of all the 
slots. At starting, both sets of coils are connected 
to the single-phase supply mains, and the difference 
between the resistance and the reactance in the two 
sets of coils splits the single-phase current supplied 
sufficiently to create a rotary field similar to that 
produced in the regular two-phase motor. This gives 
a slight starting torque, which is sufficient, however, 
to turn the rotor, but not with any considerable load. 
Hence, the load, if it is difficult to start, should be 


STARTING, SPEED CONTROL, OPERATION 


21T 


thrown on to the motor by means of a friction clutch 
after the rotor is running up to speed. The rotor 
used in the Holtzer-Cabot motor is of the squirrel- 
cage type. 

Another starting device adapted only to the smaller 
sizes of single-phase induction motors consists of a 
condenser connected in series with one phase of the 
stator windings. This will give something near 90 



Figure 115.—“Split-Phase” Method of Starting Single-Phase 

Induction Motor. 

degrees phase difference between the split-phase cur¬ 
rents. This starting device, called a condenser com¬ 
pensator, and made by the General Electric Company, 
is provided with a small auto-transformer of the step- 
up type connected in shunt with the condenser. The 
fact that a condenser for a given volt-ampere capacity 
can be constructed much more cheaply for high than 
for low voltage led to the adoption of a step-up trans¬ 
former, thus permitting the use of a condenser for 
high voltage electromotive forces. 

Figure 115 shows the connections for this type of 
starting device for a single-phase induction motoi. A, 


















218 


ELECTRIC MOTORS 


represents the auto-step-up transformer and C repre¬ 
sents the condenser. The stator windings of the motor 
are represented by D and E, while the starting wind¬ 
ing represented by B is connected to the junction of 
D and E. The motor is thus a three-phase motor at 
starting. When the rotor reaches full-rated speed, 
the starting winding B is cut out, and the winding 
DE then operates as a single-phase winding. 

(c) Shading-Coil Starting . — Another starting de¬ 
vice that is frequently used with small single-phase 
induction motors where the nature of the work is such 
that the load can be applied after the rotor is running 
up to speed, consists of what are termed shading coils. 
A shading coil consists of a single turn of copper 
placed in a slot cut in the pole face and bent around 
one side of the pole piece. The action of these shading 
coils is similar to the action of the secondary coil 
of a transformer in that its reactance upon the stator 
wunding current tends to produce a distorted field, the 
result being similar to that obtained by a split-phase 
winding. 

(d) Repulsion Motor Starting .—If an ordinary 
direct-current motor were provided with a laminated 
field magnet, and if its field magnet were excited by 
an alternating current, the result would be that cur¬ 
rents would be induced in the armature windings, pro¬ 
vided the brushes of the direct-current machine were 
set at an angle of about 45 degrees (for a two-pole 
machine) from their proper position for collecting 
a direct current. These currents induced in the arma¬ 
ture would be acted upon by the alternating field 
in such a manner as to produce a torque that would 
cause the armature to revolve. A self-starting single¬ 
phase alternating-current motor constructed on this 


STARTING, SPEED CONTROL, OPERATION 219 

principle is termed a repulsion motor. It is not en¬ 
tirely satisfactory in operation, but the repulsion-mo¬ 
tor principle furnishes the best means for making a 
single-phase motor self-starting; that is, a motor de¬ 
signed and constructed in such a manner that it can 
act as a repulsion motor while starting, and which, 
by changing certain inside connections, can be altered 
into an induction motor when it reaches full speed. 

Starting Polyphase Induction Motors. — In order 
that a polyphase induction motor may not take an ex¬ 
cessive current from the circuit to which it is con¬ 
nected when the motor is starting, either a resistance 
must be placed in the rotor circuit or the voltage im¬ 
pressed on the primary must be reduced. There are 
two general methods of starting polyphase induction 
motors, as follows : 

(a) Pressure method of starting. 

(b) Rheostatic method of starting. 

(a) The pressure method of starting consists of 
reducing and regulating the voltage impressed upon 
the primary of the motor by means of a compensator 
or auto-transformer. 

(b) The rheostatic method of starting makes use of 
the fact that a much greater torque can be produced 
by a given current when there is an extra resistance 
in series with the stator winding. This resistance 
in some small machines is located inside the rotor 
and is cut out of the circuit automatically as the ma¬ 
chine speeds up. The resistance, however, is usually 
outside of the rotor and connected in circuit with the 
rotor winding by means of collector rings and brushes. 

Reversing Induction Motors. —A single-phase motor 
will run in either direction equally well, depending 


220 


ELECTRIC MOTORS 


only upon the direction in which it is started. A 
hand started motor, therefore, can be started in either 
direction. The direction of motion of a split-phase 
motor may be reversed by reversing the connections 
of the starting winding. The direction of rotation of 
a two-phase motor may be reversed by reversing the 
connections of the two wires of either phase. To re¬ 
verse the running direction of a three-phase motor, it is 
only necessary to change any two of the phase wires. 

Speed Control of Induction Motors .—The speed of 
an induction motor may be controlled in five different 
ways, as follows: 

(a) By varying the pressure applied to the primary winding. 

(b) By varying the resistance in the secondary winding. 

(c) By changing the number of poles. 

(d) By varying the frequency of the applied pressure. 

(e) By connecting the secondary of one motor to the primary 

of another motor. 

(a) The speed control of an induction motor, by 
varying the pressure applied to the primary, is an 
elaboration of the pressure method of starting. 

(b) The speed control of an induction motor, by 
placing a resistance in the secondary circuit, is an 
elaboration of the rheostatic method of starting. 

(c) By properly designing the windings, an induc¬ 
tion motor may have its number of poles changed by 
means of a throw-over switch to which the different 
taps of the winding are connected. 

(d) Currents of different frequencies may be sup¬ 
plied from two different generators and the motors 
operated on one or the other of these circuits as the 
demands in speed may require. 

(e) If the two motors are rigidly connected to a, 
common shaft, their speed may be controlled by con- 


STARTING, SPEED CONTROL, OPERATION 221 

necting the secondary of the first motor to the primary 
of the second motor, and the controlling resistance 
in the secondary of the second motor, the primary of 
the first motor being connected to the line. This 
method of speed control is called the concatenation, 
or cascade, control. The speed of the shaft to which 
the motors are connected may be that of either motor 
acting alone, or it may be that of the two motors in 
direct or differential concatenation. Let p x represent 
the number of poles on one motor, p 2 the number of 
poles on the other motor, and / the frequency of the 
supplied current. The speed of the shaft may have 
any one of the following four values: 

Number one alone 

Number two alone 

Direct concatenation 

Differential concatenation 

Operating Characteristics of the 
—speed of the induction motor decreases in value with 
an increase in load very much like the direct-current 
shunt motor. The current taken by the motor will 
increase with an increase in load and the increase in 
the current becomes more rapid near full- or over¬ 
loads. The power factor increases very rapidly for 
low loads and should reach a maximum value near 
full load. 


x/ 

Pi 

o = 120 x/ 

Vi 

120 xf 
P1 + P2 

a_ 120x f 

P1-P2 

Induction Motor. 






CHAPTER XII 


CAEE AND OPERATION OF ALTERNATING-CURRENT 
MOTORS, AND ALTERNATING-CURRENT 
MOTOR TROUBLES 

Location .—Motors should be located in clean, dry, 
well-ventilated and easily accessible places, free from 
acid fumes, steam, dripping water, or oil, and exces¬ 
sively high temperatures. If the conditions under 
which the motor is to be operated are unusual and 
do not comply with the above-mentioned require¬ 
ments, it is best to install motors of a special construc¬ 
tion adapted to the situation. 

Foundations .—The foundation should be sufficient¬ 
ly solid to prevent excessive vibration. Masonry or 
concrete is to be preferred, but wood frame work or 
timber can be used. Wall or ceiling supports should 
be rigid. 

Erection .—The motor shaft should be level, or, if 
the motor is of the vertical type, the shaft should 
stand exactly perpendicular. If the motor is geared, 
the gears should mesh properly; if direct connected, 
the motor shaft and driven shaft must be in line, 
except for a slight variation permissible with flexible 
couplings. 

If a belt is used for transmitting power from the 
motor to the driven shaft, the driving and driven pul¬ 
leys should be aligned properly, so that the belt will 
run true. Bolt the slide rails or bed plate securely 
to the foundation and bolt the motor to the slide rails 

222 


CARE AND OPERATION 


223 


or bed plate. Key the pulley to the shaft and tighten 
the screw firmly. Turn the armature, in order to see 
that the pulley hub does not strike the bearing hous¬ 
ing, then put on the belt and tighten it by moving 
the motor by adjusting the belt adjusting screw. The 
belt should be run with, not against, the belt lapping 
and should drive on the lower side. 

Wall or Ceiling Mounting .—With motors provided 
with oil reservoirs, the brackets should be turned 
through 90 or 180 degrees, in order to keep the oil 
reservoirs directly under the shaft. 

Bearings .—If the bearings overheat, the causes may 
be one or more of the following: 

(a) Excessive belt tension. 

(b) Defective lubrication, due to either a poor grade or insuf¬ 

ficient quantity of lubricating oil, or failure of the 
oil rings to revolve. 

(c) Incorrect aligning or leveling, thereby causing excessive 

end thrust, or binding. 

(d) A rough bearing surface. 

(e) Bent shaft. 

If a bearing becomes hot, first slacken the belt, then 
feed a heavy lubricant copiously. If relief is not thus 
afforded, shut down the motor, keeping the armature 
or rotor slowly revolving until the bearing is cool, 
in order to prevent the bearing from sticking or 
‘ ‘ freezing. ’ 1 

Lubrication .—Before starting a motor, fill the oil 
reservoirs with the best quality of clean dynamo oil. 
Overflow plugs, if present, should always be kept 
open. Old oil should be withdrawn occasionally, and 
fresh oil substituted, the intervals of time for doing 
this depending upon the nature of the service the ma¬ 
chine is performing. The old oil can be filtered and 


224 


ELECTRIC MOTORS 


used again. If the oil is fed to the bearings by wicks, 
or oil feeding cups, the drip of oil from the bearings 
will show that they are in order. Ring oiling is much 
used at present and is, in fact, much more reliable 
than other systems, but the rings should be watched 
to see if they move properly around the journals. 

These rings are several times the diameter of the 
journal or axle and hang upon it, their lower portions 
dipping into the oil reservoir in the lower portion 
of the bearing housing. As the shaft revolves, they 
travel around it, thus carrying oil to the upper surface 
of the journal. When cleaning out the old oil and 
before adding new oil, the oil reservoirs should be 
washed out with kerosene oil. A small syringe is very 
useful for this purpose. Oil should be carefully kept 
off the brush holders, commutator surface, and the 
winding of armature and field. 

Safety Fuses .—These should be inspected at fre¬ 
quent intervals to see if they are tightly screwed 
down or clamped, and also if their contact faces are 
clean. 

Insulation .—A careful watch should be made for 
bare spots or weak spots on the insulation of all wires 
in the windings. If there are any indications of such 
defects, they should be immediately taped or insulated 
in some way. 

Broken Wires .—A broken wire can be detected by 
the feeling, even if it is thickly insulated, by slightly 
bending or moving the wire. If there are any indica¬ 
tions of burning or overheating of the insulation, a 
fracture of the wire may be suspected at that point. 

Soldering Wires .—Acid should never be used in 
soldering wires together. For this purpose, anti-cor¬ 
rosive soldering fluxes may be procured, which can be 


CARE AND OPERATION 


225 


used on iron or copper, and will answer the purpose as 
well as acid, and thus eliminate any bad after effects 
of corrosion due to the use of acid. 

Idle Motors. —When a motor is doing no work, the 
current should be cut off. A motor running without 
load draws energy from the circuit which must be 
paid for. 

Collector Rmgs. —The collector rings on alternat¬ 
ing-current machines should be kept bright and clean. 
A little vaseline applied from time to time is good 
practice. If the surface is rough, the machine should 
be stopped, the brushes lifted off, the armature or 
rotor started turning again, and the rings be sandpa¬ 
pered, using a hollowed block of wood to hold the 
sandpaper. 

Local Heating of Stator Windings. —This, in an 
induction motor, indicates a double short-circuit, 
either in a single coil or in two neighboring coils. 
If wound for Y distribution, an interruption of one 
phase will interfere with the running of the machine. 
If the load is light, the motor may go on as a synchro¬ 
nous motor. Sometimes the beginning and end of a 
coil are interchanged in their connection, so as to re¬ 
duce the phase difference to 60 degrees. This inter¬ 
feres with the running of a three-phase Y-connected 
motor. 

If one phase of the primary is open, the motor will 
not start and the current will be unbalanced. 

If one phase of the primary is reversed, the current 
will be very much unbalanced when the motor is 
running, and there will be very little starting torque. 

Induction-Motor Rotors. —The short-circuited self- 
contained rotor of the modern induction motor seldom 
gives trouble. In the older types, the rotor would 


226 


ELECTRIC MOTORS 


sometimes become so hot as to melt the solder on the 
winding connections, thus opening the circuit and 
causing the machine to stop. Good modern practice 
uses no solder on the connections, but, by hard metal 
couplings or brazing, secures heat-proof joints. 

If the secondary winding of the motor is open, the 
motor will not start and it will not take a current 
greater than the exciting current. 

If one phase of the secondary winding is open, the 
motor has a tendency to operate at one-half speed, 
although the current may be apparently normal. If 
the current in the three phases is measured, when the 
rotor is blocked, it will be found unbalanced. 

Starting and Speed Regulation .—Synchronous mo¬ 
tors, whether single-phase or polyphase, should be 
speeded up before the load is thrown on, and this 
should be gradually applied only when full speed is 
attained. If overloaded, the motor will stop. This 
type of motor will maintain a constant speed (syn¬ 
chronous) and will run at no other. 

Polyphase induction motors which can carry an 
overload within certain limits, lose in speed as the load 
is increased, but are self-starting, even with a load. 

Cleaning a Machine .—Cotton waste should be care¬ 
fully used in cleaning a motor or generator, as threads 
from it will catch in and stick to the commutator and 
other surfaces. Dust can be blown out of inaccessible 
places with a hand bellows, or, in case compressed air 
is available, a small air hose can be used. 

Starting Induction Motors .—Small size induction 
motors—3 to 5 hp.—may be started by connecting 
the stator terminals directly to the line, but with the 
larger sizes the inrush of current is excessive, and a 
starting compensator, or some other form of starting 


CARE AND OPERATION 


22- 


device, is usually necessary in order to prevent too 
great a disturbance of the system. 

Speed Regulation for Induction Motors. —For some 
classes of work, it is desirable to arrange induction 
motors in such a manner that their speed can be 
controlled, the usual methods being either the inser¬ 
tion. of a variable resistance in the rotor circuit or 
cutting down the voltage of the current applied to the 
stator windings. Both methods are explained in an¬ 
other section of this book. 

A two- or three-phase induction motor will operate, 
fairly well, if, after it has reached full speed, all but 
one of the phases be cut out. It will not, however, 
start from rest with only single-phase excitation. 

Safety Precautions. —Keep all tools and pieces of 
iron or steel away from the machine while running, 
as they might be drawn in by the magnetism and 
perhaps get between the rotor and stator, and thus 
ruin the machine. For this reason it is safest to use 
a zinc, brass, or copper oil can, instead of one of iron 
or “tinned” iron. Never allow your body to form 
part of a circuit. While handling a conductor, a 
second contact may be accidentally made through the 
feet, hands, knees, or other part of the body, in some 
unexpected manner, the result being fatal. Rubber 
gloves or rubber shoes, or both, should be worn when 
handling circuits of over 500 volts. The safest plan is 
not to touch any conductor carrying a current. Tools 
with insulated handles, or a dry stick of wood, should 
be used instead of the bare hands. If possible, use 
only one hand when handling dangerous conductors, 
because by so doing there is not so much danger of 
getting the current through the body. The rule, keep 
one hand in your pocket, is a good rule to remember 


pi6 


ELECTRIC MOTORS 


vvlmn working around electric machines or highly 
charged circuits. Short-circuits between armature 
windings and frame are dangerous not only to the 
machine but to the life of the attendant if a grounded 
circuit is on the line. A 110-volt current has killed 
in several recorded cases. A good practice is to 
ground the frame of an alternating-current machine; 
then if a man touches the frame of a machine in 
which a dangerous short-circuit exists, he is simply 
in parallel with a portion of the frame and receives 
no injury. Were the frame not grounded, the man 
might he killed. If no ground circuit exists on the 
line, such a contact of windings and frame may re¬ 
main undiscovered indefinitely, unless closely watched 
for. It is a good plan to inspect and test the machines 
at intervals for the purpose of ascertaining if such 
dangerous conditions actually exist, and, if so, to 
remedy them. 


Specific Resistance, Temperature Coefficient, Percent Relative Resistance and Con 

DUCTANCE OF DIFFERENT MATERIALS 


r 


APPENDIX 


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ts.8 

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229 

































230 


ELECTRIC MOTORS 


TABLE II 

COPPER WIRE TABLE 

Working Table, International Standard Annealed 

Copper 

American Wire Gage (B. & S.) 




Cross Section 

Ohms per 1000 
Feet 





c a 






00 

<D 







,d 




6 

£ 

<D 

bC 

cS 

iameter in 
Mils 

• r-» 

a 

Jh 

oj 

d 

o 

t-C 

• rH 

o 

d 

i—i 

<D 

(H 

& 

o 

o 

o l> 

to t- 
ca || 

S' 

O o 

05 
o ^ 

IO tH 

® II 

ounds per 

000 Feet 

o 

ft 

O 

m 





0000 

460. 

212 000. 

0.166 

0.0500 

0.0577 

641. 

000 

410. 

168 000. 

.132 

.0630 

.0727 

508. 

00 

365. 

133 000. 

.105 

.0795 

.0917 

403. 

0 

325. 

106 000. 

.0829 

.100 

.116 

319. 

1 

289. 

83 700. 

.0657 

.126 

.146 

253. 

2 

258. 

66 400. 

.0521 

.159 

.184 

201. 

3 

229. 

52 600. 

.0413 

.201 

.232 

159. 

4 

204. 

41 700. 

.0328 

.253 

.292 

126. 

5 

182. 

33 100. 

.0260 

.319 

.369 

100. 

6 

162. 

26 300. 

.0206 

.403 

.465 

79.5 

7 

144. 

20 800. 

.0164 

.508 

.586 

63.0 

8 

128. 

16 500. 

.0130 

.641 

.739 

50.0 

9 

114. 

13 100. 

.0103 

.808 

.932 

39.6 

10 

102. 

10 400. 

.008 15 

1.02 

1.18 

31.4 

11 

91. 

8230. 

.006 47 

1.28 

1.48 

24.9 

12 

81. 

6530. 

.005 13 

1.62 

1.87 

19.8 

13 

72. 

5180. 

.004 07 

2.04 

2.36 

15.7 

14 

64. 

4110. 

.003 23 

2.58 

2.97 

12.4 

15 

57. 

3260. 

J002 56 

3.25 

3.75 

9.86 

16 

51. 

2580. 

.002 03 

4.09 

4.73 

7.82 

17 

45. 

2050. 

.001 61 

5.16 

5.96 

6.20 

18 

40. 

1620. 

.001 28 

6.51 

7.51 

4.92 

19 

36. 

. 1290. 

.001 01 

8.21 

9.48 

3.90 

20 

32. 

1020. 

.000 802 

10.4 

11.9 

3.09 












APPENDIX 


231 


o 

fc 

9 

tD 

03 

o 


.3 


!j 03 


<D Jsi 
c3 


Cross Section 


in 


t- 

• pH 

O 


X 

<D 


o> 

I— 


cr 

m 


Ohms per 1000 
Feet 


o ^ 

o 

o t— 
lO t- 

03 II 


U° 

Cl 

o 

lO *H 

«o II 


<3 -M 

Q. © 
X [V, 

1=1 2 
2 2 
O o 

Oh 


21 

28.5 

810. 

.000 

636 


13.1 

15.1 

2.45 

22 

25.3 

642. 

.000 

505 


16.5 

19.0 

1.94 

23 

22.6 

509. 

.000 

400 


20.8 

24.0 

1.54 

24 

20.1 

404. 

.000 

317 


26.2 

30.2 

1.22 

25 

17.9 

320. 

.000 

252 


33.0 

38.1 

0.970 

26 

15.9 

254. 

.000 

200 


41.6 

48.0 

.769 

27 

14.2 

202. 

.000 

158 


52.5 

60.6 

.610 

28 

12.6 

160. 

.000 

126 


66.2 

76.4 

.484 

29 

11.3 

127. 

.000 

099 

5 

83.4 

96.3 

.384 

30 

10.0 

101. 

.000 

078 

9 

105. 

121. 

.304 

31 

8.9 

79.7 

.000 

062 

6 

133. 

153. 

.241 

32 

8.0 

63.2 

.000 

049 

6 

167. 

193. 

.191 

33 

7.1 

50.1 

.000 

039 

4 

211. 

243. 

.152 

34 

6.3 

39.8 

.000 

031 

2 

266. 

307. 

.120 

35 

5.6 

31.5 

.000 

024 

8 

335. 

387. 

, .0954 

36 

5.0 

25.0 

.000 

019 

6 

423. 

488. 

.0757 

37 

4.5 

19.8 

.000 

015 

6 

533. 

616. 

.0600 

38 

4.0 

15.7 

.000 

012 

3 

673. 

776. 

.0476 

39 

3.5 

12.5 

.000 

009 

8 

848. 

979. 

.0377 

40 

3.1 

9.9 

.000 

007 

8 

1070. 

1230. 

.0299 


NOTE—The table is based on the international standard of re¬ 
sistance for copper, which takes the fundamental mass resistivity 
= 0.15328 ohm (meter, gram) at 20° C, the corresponding tempera¬ 
ture coefficient = 0.00393 at 20 c C, and the density = 8.89 grams 
per cc at 20° C. The temperature coefficient is proportional to the 
conductivity, whence the change of mass resistivity per degree C 
is a constant, 0.000597 ohm (meter, gram). 

NOTE 2—The values given in the table are only for annealed 
copper of the standard resistivity. The user of the table must apply 
the proper correction^for copper of any other resistivity. Hard- 
drawn copper may be taken as about 2.7 per cent higher resistivity 
than annealed copper. 

NOTE 3—Ohms per mile, or pounds per mile, may be obtained by 
multiplying the respective values above by 5.28. 

NOTE 4—For complete tables and other data see Circular No. 1(1 
Of the Bureau of Standards. 





















INDEX 


PAGE 

A 

Alternating-current electrical circuits. 40 

alternation . 42 

cycle. 42 

divided . 50 

effect of capacity in. 47 

effect of inductance in. 46 

frequency . 42 

instantaneous power in . 50 

maximum, average, and effective values of current. 44 

Ohm’s law for. 45 

period . 42 

phase displacement. 43 

resistance, inductance, and capacity, combined effects 

of in . 48 

series . 49 

single-phase circuit. 53 

synchronism . 43 

true power in. 52 

two-phase circuit. 54 

Alternating-current motors 

armature windings for.157 

armature conductors, types of.160 

armature cores, classification of.158 

d. c. and a. c. armature windings compared.158 

single-phase -windings.161 

stationary and rotating armatures.157 

three-phase windings .167 

two-phase windings.163 

care and operation* and troubles.222 

bearings .223 

broken wires .224 

cleaning a machine.226 

collector rings .225 

erection .222 


































INDEX 


Alternating-current motors fAUL 

foundations .222 

idle motors. 225 

induction-motor rotors .225 

insulation .224 

local heating of stater windings.225 

location .,.222 

lubrication . 223 

safety fuses .224 

safety precautions .227 

soldering wires .224 

starting induction motors.226 

starting and speed regulation.226 

wall or ceiling mounting.223 

commercial types of.171 

commutator motors.194 

general classification .171 

induction motor.183 

synchronous motors .172 

starting, speed control, operation.204 

methods of starting.204 

operating characteristics of .221 

phase characteristics of synchronous motor.214 

reversing induction motors.219 

self-starting of polyphase synchronous motors.204 

speed control of induction motors.220 

speed control of synchronous motors.214 

starting compensator .206 

starting polyphase induction motors.219 

starting single-phase induction motor.215 

hand starting.215 

repulsion motor.218 

shading-coil starting . 218 

split-phase starting .215 

windings of compensators.209 

Alternating electromotive force, definition of. 40 

Alternation. 42 

Ammeter. 56 

Apparent power . 53 

Appendix .229 

Armature cores, types of. 68 

disk armature. 69 

drum armature . 69 

ring armature . 68 

Armature reaction in motor.100 

means of reducing.110 















































INDEX 


Armature windings for 

a.c. motors . 257 

d.c. motors . gg 

armature cores, types of. ' gg 

brush sets required. 7 g 

electromotive force generated in. 7(3 

element of. gy 

paths through, number of. 7 g 

two-layer windings . yg 

windings, types of ... ' g 9 


Bar winding 


,161 


C 


Capacity, effect of in a.c. circuit. 47 

Capacity reactance . 46 

Closed-coil windings.•. 69 

Coefficient of dispersion. 94 

Commutating plane .103 

Commutation .106 

Commutator motors .194 

action of d.c. series motor when supplied with alternating 

current . 195 

action of d.c. shunt motor wffien supplied with alternating 

current . 194 

commutation of series a.c. motor, methods of improving. .196 

compensating windings .198 

repulsion motor .199 

Commutator pitch . 71 

Compensators 

starting .206 

windings of .209 

Compound motor. 97 

Conductance . 18 

Conductor . 70 

Counter-electromotive force .114 

Current 

definition of. 40 

measurement of. 56 

of electricity . 10 

Current transformer . 57 

Cycle . 42 



































INDEX 


PAGE 

D 

Direct-current electrical circuits . 9 

calculation of resistance . 12 

current of electricity . 10 

electrical pressure . 10 

electrical work or energy. 20 

mechanical and electrical power. 21 

parallel or divided circuits. 17 

resistance of circuit . 10 

series circuits. 15 

typical. 0 

Direct-current motors .124 

care and operation and troubles.146 

bearings ... • 150 

belts .152 

brushes .147 

changing direction of rotation.156 

commutator .148 

general rules . 146 

heating of armature.149 

heating of commutator .149 

heating of field coils.149 

refusal of motor to start.153 

shut down constant-speed motors.152 

shut down series motors.152 

shut -down variable-speed motors.152 

sparking .148 

sparking at brushes .155 

speed of motor too high.155 

speed of motor too slow.154 

starting constant-speed motors.151 

starting series motors.152 

starting variable-speed motors.152 

static sparks from belts.153 

commercial types of. 80 

armature reaction in .100 

brushes, proper position of on.102 

commutation.106 

counter-electromotive force.114 

cross-magnetizing ampere-turns .105 

demagnetizing ampere-turns.104 

excitation of . 95 

Fleming’s left-hand rule. 80 

fundamental principle of. 80 

generator and motor interchangeable. 81 














































INDEX 


Direct-current motors page 

magnetic fields, types of. 90 

magnetic leakage . 94 

materials used in construction of magnetic circuit of 

motor. 93 

mechanical output of motor.115 

multiple-coil armatures. 85 

normal speed .118 

starting. 119 

starting boxes . 121 

two-part commutator, operation of. 82 

efficiencies of.142 

losses in. . . 141 

operating characteristics of.136 

compound motor . 139 

series motor .138 

shunt motor. 137 

speed control, regulating.124 

by change in magnetic flux.124 

by series-parallel connections .132 

by varying position of brushes.130 

by varying voltage impressed on armature terminals. . .127 

Disk armature .69, 158 

Divided a. c. circuit. 50 

Drop in potential method of measuring resistance. 59 

Drum armature.69, 158 

Duplex winding . 73 


E 


Eddy currents . 38 

Electrical circuits 

alternating-current . 40 

direct-current. 9 

Ohm’s law for. 11 

resistance of . 10 

series . 16 

Electrical measurements of. 56 

current . 56 

power . 64 

in three-phase circuit. 66 

in tw’o-phase circuit. 65 

pressure. 58 

resistance .*.. 59 

Electrical pressure . 10 

Electrical work or energy . 20 









































INDEX 


PAGE 

Electricity, current of. 10 

Electromagnetic induction . 36 

Electromotive force and current, maximum, average, and 

effective values of. 44 

Electromotive force generated in armature winding. 76 

Energy . 20 

Excitation of direct-current motors. 95 

F 

Field intensity. 34 

Fleming’s left-hand, or motor, rule. 80 

Frequency. 42 

G 

Gilbert . 32 

H 

Henry . 38 

Hunting of synchronous motor.177 

Hysteresis . 35 

Hysteresis loss. 35 

Hysteretic constant K, value of, for different materials. ... 36 

I 

Impedance . 46 

Indicating wattmeter. 65 

Inductance . 37 

effect of in an a.c. circuit. 46 

Induction density . 34 

Induction motor .183 

as a frequency changer.193 

construction of .187 

fundamental principle of.186 

induction generator .193 

operation of.189, 222 

reversing .219 

rotating magnetic field .183 

slip of rotor.190 

speed of .189 

speed control of.*.... .220 

speed regulation for.227 

starting .219, 226 

torque of....191 

Inductive reactance . 46 

Instantaneous power in a.c. circuit. 50 





































INDEX 


PAGE 

J 

Joule . 21 

L 

Laminations . 38 

Lap and wave windings. 70 

M 

Magnet . 25 

Magnetic circuit 

Ohm’s law for. 33 

reluctance of .’.. 32 

Magnetic cycle . 36 

Magnetic field . 26 

produced by a current. 27 

solenoid. 29 

types of. 90 

Magnetic flux . 31 

Magnetic force, lines of. 26 

Magnetic leakage . 94 

Magnetic poles . 25 

Magnetic substance . 25 

Magnetism . 25 

Magnetization curves. 34 

Magnetomotive force . 31 

Mil-foot resistance ... 13 

Multiple-coil armatures. 85 

Mutural inductance . 38 

N 

Negative terminal. 15 

O 

Oersted . 32 

Ohm’s law for 

alternating-current circuit. 45 

electrical circuit . 11 

magnetic circuit..T. 33 

Open-coil windings. 09 

P 


Parallel or divided circuits 

Period . 

Permeability . 


. . .. 17 
. ... 42 
32, 34 

































INDEX 


PAGE 

Phase displacement. 43 

Pole face . 92 

Pole tips. 92 

Positive terminal. 15 

Potential transformer . 59 

Power 

measurement of. 64 

mechanical and electrical. 21 

Power factor.53, 65 

Pressure, measurement of. 58 

R 

Eeactance . 46 

Reluctance . 32 

Repulsion motor .199 

Resistance 

calculation of . 12 

changes of with temperature. 14 

of electrical circuit. 10 

measurement of 

drop in potential method. 59 

series-voltmeter method. 61 

by Wheatstone bridge . 63 

Resistance, inductance, and capacity, combined effects of in 

a.c. circuit . 48 

Ring armature .68, 158 

Rotor of induction motor.188 


S 

Self-inductance . 38 

Series a.c. circuit . 49 

Series d.c. circuits . 15 

Series motors. 96 

Series-voltmeter method of measuring resistance.;. 61 

Shunt motors. 95 

Simplex winding. 73 

Single-phase circuit . 53 

Solenoid . 29 

polarity of..•. 30 

Sparking.148 

Starting compensator.206 

Stator of induction motor.187 

Strap wunding . 160 

Synchronism . 43- 






































INDEX 


PAGE 

Synchronous motors .172 

adjustment of current in armature winding of.175 

field excitation and power factor.178 

fundamental principle of.172 

hunting of . 177 

phase characteristics of.214 

phase-modifier .181 

speed of . 174 

speed control of.214 

T 

Table 

copper -wire .230 

hysteresis constant K, value of, for different materials. ... 36 
specific resistance, temperature coefficient, etc., of differ¬ 
ent materials .229 

Temperature coefficient . 14 

Torque . ... 115 

Triplex winding . 75 

True power in a.c. circuit. 52 

Two-phase circuit . 53 

V 

Voltmeter . 58 

Voltmeter-ammeter method of measuring power. 64 

W 

Watt . 22 

Wattmeter . 65 

Wheatstone bridge . 63 

Winding element . 69 

Winding pitch . 71 

Windings, types of 

closed-coil . 69 

open-coil . 69 

Wire table .230 

Wire winding .160 







































ELECTRICAL 
OPERATING AND 
TESTING 


















TABLE OF CONTENTS 


CHAPTER I. Page 

The Electric Current . ? 

CHAPTER II. 

Electrical Units . 14 

CHAPTER III. 

Magnetism . 19 

CHAPTER IV. 

Principles of Dynamo Electric Machines. 39 

CHAPTER V. 

Types of Dynamos . 56 

CHAPTER VI. 

Principles of Electric Motors—Direct Current. 14 

CHAPTER VII. 

Types of Motors—Direct Current . 80 

CHAPTER VIII. 

Principles of Alternating Current Motors. 86 

CHAPTER IX. 

Types of Motors—Alternating Current . 96 

CHAPTER X. 

Dynamo Operation—Direct Current .10 -j 

CHAPTER XL 

Operation of Alternators.124 

CHAPTER XII. 

Motor Operation . 145 

V 














vi Table of Contents 

CHAPTER XIII. 

Transformers .151 

CHAPTER XIV. 

Batteries .170 

CHAPTER XV. 

Arc Lamps .184 

CHAPTER XVI. 

Incandescent Lamps .217 

CHAPTER XVII. 

Nernst and Cooper Hewitt Lamps.239 

CHAPTER XVIII. 

Instruments for Testing .243 

CHAPTER XIX. 

Testing .269 

CHAPTER XX. 

Dynamo and Motor Troubles .298 

CHAPTER XXI. 

Recording Wattmeters .307 

CHAPTER XXII. 

Life and Fire Hazard .342 

CHAPTER XXIII. 

Ground Detectors and Lightning Arresters.347 













. CHAPTER I 


THE ELECTRIC CURRENT 

By the electric current is meant that agency which 
comes into action when a circuit containing an elec¬ 
tro-motive force is closed. Electro-motive force is, as 
the name implies, the impelling force, and the circuit 
is the system of conductors along which alone elec¬ 
trical action takes place. This flow of current is quite 
analogous to the flow of water in a system of piping 
or over the surface of the earth. Such a flow of water 
can take place only when the water is at different lev¬ 
els, or, when from any cause, a difference of pressure 
exists between different points. When either or both 
of these conditions exist the flow always takes place in 
a certain direction,n. e., from the high level or pressure 
to the lower, and this flow is always more or less dimin¬ 
ished by obstacles or resistances. The same observa¬ 
tions hold true of electric currents; they flow only in 
obedience to electrical pressure; they flow always in 
a certain direction determined by that pressure and 
the quantity of the flow depends, or is governed, other 
things being equal, by obstacles which are spoken of 
as resistances. 

We cannot prove, and it is not necessary, that there 
"s any actual direction, or, much less, a change of direc- 


7 


8 


Operating and Testing 


tion, or even a flow of current, but the phenomena no¬ 
ticed make the assumption a very convenient one and 
it is, to say the least, very helpful in the study and 
application of these phenomena. 

Refer now to Figure 1 which shows a common glass 
jar nearly filled with water and which also contains 
a small quantity of sulphuric acid and one plate of 
zinc Z and another of copper C. While the two ends 
of the wires connected to the plates remain apart 
there is no flow of current, but an electrical pressure 



exists, as can readily be shown. As soon, however, aa 
we bring the two ends of wire together a flow of cur¬ 
rent takes place. It is the high resistance of the air 
between the two terminals of the wires which prevents 
the flow of current in this case, just as the resistance 
of the valve in a water pipe prevents the flow of 
water when it is closed. 

The direction of the flow of current is said to be 
from the zinc to the copper inside of the cell and from 
the copper back to the zinc m tne exterior circuit or 








The Electric Current 


9 


outside of the cell. In all batteries (a battery is a 
number of cells coupled together) the copper plate or 
terminal is spoken of as the positive or + pole from 
which the current flows and the zinc plate as the neg¬ 
ative or — pole toward which the current flows. From 
the cell shown, which is the simplest of all forms, we 



can obtain but a very insignificant current, and that 
for only a very short time, for reasons to be given 
later on. If we couple a number of cells together, as 
conventionally indicated at B in Figure 2, we shall be 
able to obtain a considerable current. In this repre¬ 
sentation of a battery the lon^r thin lines stand for 
the copper plate from which the current flows to the 

























































10 


Operating and Testing 


outside circuit and the short thick lines stand for the 
zinc element from which the current flows inside of 
the cell to the copper element. 

Figure 2 has been drawn principally to acquaint 
the reader with the general effects obtainable from the 
electric current. In the outer system of wires W, W, 
etc., the same current passes through all of the de¬ 
vices, and this is known as a series circuit. R repre¬ 
sents fine wire, which will be heated to redness or 
even melted if the current is made strong enough. At 
A is shown the manner in wdiich an arc or a flash 
may be produced; first bring the ends of carbon or 
metal together until the current is started, then sep¬ 
arate them a little and the current will continue, thus 
forming a very hot flame known as the electric arc. 

If a wire carrying a current be wound about an 
iron core M, magnetism will be generated and enable 
the iron bar to attract other pieces of iron. This 
magnetism will exist only wdiile the current is flowing. 

If the current is forced to pass through water, as 
indicated at E, it will decompose it and this decompo¬ 
sition wdll be noticeable by the bubbles of gas given 
off. If the current pass through a suitably prepared 
bath in which metals are properly connected to the 
wires, the metal wdll be eaten awny from the positive 
pole and deposited at the negative. 

The arrangement of wires shown at I, I 1 is drawn to 
illustrate the method of inducing currents of electric¬ 
ity in transformers. When a current is passed around 
the bar at I a current wdll be induced in I'. This 
current will last only a very short time, but if I is 
connected to a circuit in which the current is contin- 


The Electric Current 


11 


ually changing in value the induction of currents will 
follow every change in current strength and it is pos- 
- sible to arrange these variations in such a manner that 
light may be obtained from these induced currents. 

The inner circuit shown connected to the battery by 
heavy lines is known as a parallel circuit, all of the 
devices being connected in parallel instead of in series 
as in the other. In such a circuit each device is inde¬ 
pendent of the others and the current increases in 
proportion to the needs of the devices connected. The 
more there are connected the greater becomes the cur¬ 
rent, but the voltage need not be increased. In a se¬ 
ries circuit the more devices there are connected the 
more cells of battery must be provided to increase the 
pressure so that the current may remain the same. 
Only such devices as use the same amount of current 
can be run in a series circuit. 

In the parallel circuit at C there is shown a con¬ 
denser. A condenser is an arrangement of plates 
which is capable of taking a charge of electricity at 
rest much as a jar is capable of taking a charge of 
water. The positive and negative plates of a con¬ 
denser are perfectly insulated from each other and a 
current of electricity cannot pass from one to the 
other. When, however, the plates are connected to a 
source of current a small quantity of current will pass 
into the condenser. Such a charge may be held in a 
condenser for some time or will pass out of it when 
the voltage at the terminals is withdrawn or the circuit 
around the condenser closed. Enough current can be 
made to pass in and out of a small condenser to affect 
a telephone receiver T, or a sensitive polarized bell. 


12 


Operating and Testing 


CONDUCTORS AND INSULATORS 

An appreciable current flow can take place only in 
a system of electrical conductors. The best conductors 
are the various metals in the order here given: silver, 
copper, gold, platinum, tin, lead, etc. The difference 
in favor of silver as against copper is so small com¬ 
pared to the higher price of silver that the latter is 
seldom used. A pound of copper will, under the same 
circumstances, carry about 6 or 7 times as much cur¬ 
rent as a pound of iron and as this fact makes copper 
much cheaper than iron, copper is the metal almost 
universally used for electrical purposes. 

It is not, however, sufficient to provide conductors 
along which the current can flow; it is also necessary 
to surround these conductors with some material which 
will prevent the current from flowing anywhere ex¬ 
cept along these conductors. A bare copper wire lying 
on some other conducting material can no more be 
depended upon to carry the current than a lot of 
broken or disconnected pipes can be depended upon 
to carry a stream of water. Even under such condi¬ 
tions the current may flow along the wires and the 
water may flow along the pipes if these happen to 
offer the easiest path, but in neither case will it be 
possible to get any work done. To get the proper 
service from either we must be able to force the flow 
where our machinery needs it; whatever portion of it 
we can not so confine is a direct loss. 

Such materials as resist the flow of current suffi¬ 
ciently to prevent its' escape from the conductors in 
appreciable quantities are known as insulators. Some 


The Electric Current 


13 


of them are: air, glass, silk, rubber, dry asbestos, 
porcelain, slate, marble, wood, mica, shellac, paraffine, 
etc. All insulators to give the best service require to 
be dry. If they are wet current will leak through the 
body of those that are porous and over the surface 
of those that are not. It should be borne in mind that 
there is no such thing as, either a perfect conductor 
or a perfect insulator. Every conductor offers some 
resistance to the flow of current and no matter what 
the msulator may consist of, if we but make the pres¬ 
sure great enough we can force some current 
through it. 


CHAPTER II 


ELECTRICAL UNITS 

In order to make any practical use of electricity we 
must be able to measure it, and for the purpose of 
measurement and calculation the following units have 
been adopted by electricians, and in turn legalized by 
the U. S. government: 

The ohm as the unit of resistance. 

The ampere as the unit of current flow or current 
strength. 

The volt as the unit of electro-motive-force or elec¬ 
trical pressure. 

The coulomb as the unit of quantity. 

The farad as the unit of capacity. 

The joide as the unit of work. 

The watt as the unit of power. 

The henry as the unit of induction. 

THE OHM 

The ohm is the unit of resistance. Resistance is a 
property possessed by all materials, but in varying de¬ 
grees. It always varies inversely as the cross-section 
of the material; that is, the larger the wire the less 
will be its resistance and the smaller the wire the 


14 


Electrical Units 


15 


greater will be its resistance. The resistance of all 
materials increases directly as the length, and is, also, 
to a small extent, affected by a rise in temperature. 
This resistance acts electrically much as friction does 
mechanically; it is very useful in the proper place 
and very objectionable in the wrong place. It is this 
resistance in the filament of a lamp that gives us light 
when current is forced through it, and heat in the 
heater, but it is also this resistance which causes the 
loss in voltage or pressure which makes it so difficult 
to transmit currents of magnitude over wide areas. 
Resistance tends to diminish current flow and, when 
great enough, prevents it entirely. 

The legal ohm is equivalent to the resistance of a 
column of mercury 106.3 centimeters long, 14.4521 
grammes in mass and at the temperature of melting 
ice. As an illustration of more practical value: 2 3/10 
feet of No. 36 B. & S. gauge wire has a resistance of 
one ohm; 380 feet of No. 14 wire a resistance of one 
ohm and 1,000 feet of No. 10 wire a resistance of one 
ohm. 

THE AMPERE 

The ampere is the unit of current strength. It ex¬ 
presses the rate of current flow. It is not correct to 
speak of it as measuring quantity. To obtain the 
quantity we must multiply the amperes flowing by the 
length of time they flow. The heating of a wire, the 
chemical action and the magnetism produced are all 
due to the amperes flowing in the circuit. The legal 
ampere is that current, which, when passed through 
a solution of nitrate of silver, prepared in accordance 


16 


Operating and Testing 


with certain specifications, deposits silver at the rate 
of 0.001118 grammes per second. 

It is the current which results from a pressure* of 
one volt acting in a closed circuit on a resistance of 
one ohm. A 16 c. p. 110 volt incandescent lamp re¬ 
quires a current of one-lialf ampere; an open, series 
arc lamp a current of about 10 amperes. 

THE VOLT 

The volt is the unit of electro-motive-force, or elec¬ 
trical pressure. It is this pressure which is the imme¬ 
diate cause of current flow and we speak of it as of so 
many volts, just as we speak of steam pressure as of 
so many pounds. 

The volt is defined as the electro-motive-force which 
will force a current of one ampere through a resist¬ 
ance of one ohm. This is equal to about 1000/1434 
of the electro-motive-force of a Clarkes cell. The com¬ 
mon wet carbon battery gives about 1.2 volts; a stor¬ 
age battery about 2 volts per* cell. 

THE COULOMB 

The coulomb is the unit of quantity. It is the cur¬ 
rent delivered by one ampere in a second. To find the 
number of coulombs we multiply the number of am¬ 
peres by the time in seconds. This unit is seldom used. 

THE FARAD 

The farad is the unit of capacity. Under certain 
circumstances electrical conductors and certain ap¬ 
pliances chiefly known as condensers can be heavily 
charged with static electricity (electricity in a state 
of rest) and can be again discharged; and, in fact if 


Electrical Units 


17 


subjected to an alternating electro-motive-force this 
charging and discharging is continually taking place. 
This charge depends upon the nature of the material 
out of which the condenser is made upon the number 
and size of the plates and upon the electro-motive-force 
of the circuit. The more current there is forced into 
a given condenser the greater will be its potential dif¬ 
ference. This can not, of course, be greater than that 
maintained at its terminals unless a static charge be 
given. 

Such a conductor or condenser is said to have a ca¬ 
pacity of one farad, when a charge of one coulomb 
produces a difference of potential of one volt. This 
unit comes into use very seldom in ordinary work. 

THE JOULE 

The joule is the unit of work. It is equal to the 
energy expended in forcing one ampere through a re¬ 
sistance of one ohm, in one second. This unit is also 
seldom used. 

THE WATT 

The watt is the unit of power. Just as the ampere 
expresses the rate of current flow, without telling us 
anything about the actual quantity delivered, so the 
watt measures the rate of doing work, or the rate of 
energy consumption in the circuit. The watts in any 
circuit are equal to the volts multiplied by the am¬ 
peres. An incandescent lamp requiring 110 volts and 
% ampere is said to consume energy at the rate of 
55 watts. Seven hundred and forty-six watts equal 
one horsepower. The watt is a much used unit and 
charges for use of light or power are usually based 


18 


Operating and Testing 


upon watt-hours. The watts supplied, multiplied by 
the time, measure the power delivered. 

THE HENRY 

The henry is the unit of induction. It is seldom 
used in ordinary practical calculations but an under¬ 
standing 1 of its meaning is important. 

The henry represents the induction in the circuit 
when the induced electro-motive-force is equal to one 
volt while the inducing current varies at the rate of 
one ampere per second. 


CHAPTER III 


MAGNETISM 

The simplest form of magnet and also the one with 
which people are most familiar is the compass needle. 
This needle is merely a bit of magnetized steel and 
has the property of pointing toward the north with 
one of its ends and, of course, south with the other. 
Such a compass needle is a very convenient instru¬ 
ment to have about and many instructive little ex¬ 
periments can be made with it. If we take a compass 
and explore any piece of steel that has been lying in a 
north and south direction, as, for instance some por¬ 
tion of a steel building, we shall quickly see that the 
north end of the piece of steel has a tendency to repel 
the north seeking end of the needle, but will attract 
the south seeking end of the same needle with as 
much force as it repelled the other end. In making this 
experiment and in all other similar experiments care 
must be exercised not to bring the needle, especially 
if it should not be free to swing, too close to the bar 
of steel, if this be strongly magnetized, otherwise the 
powerful magnetism of the bar may overpower that 
of the needle and reverse its polarity. In such a case 
the former north seeking end would become the south 
seeking end. 


19 


20 


Operating and Testing 


We have mentioned the needle and the bar as being 
made of steel because steel differs from iron in that it 
has the power to retain whatever magnetism it may be 
charged with for an indefinite time, while iron, espe¬ 
cially if it be well annealed and soft, looses its mag¬ 
netism the instant the magnetizing force ceases to act. 
A bar of iron will attract the needle as well as the 
steel but to a lesser extent ; with the steel bar the at¬ 
tracting or repelling force will be due to the action of 
both magnets while with the iron bar it will be only 
the force of the needle that does the attracting. 

Magnets consisting of hardened steel are known as 
permanent magnets and usually made up either in 



Figure 3 

horse-shoe shape or in the form of straight bars as 
shown in the following figures. It is impossible to 
make a magnet with one pole only. No matter into 
how many pieces we may divide a magnetized bar. 
each piece will possess a north and a south pole. This 
is illustrated in Figure 3 where the different poles are 
designated by the iron filings which cling to them. If 
these pieces be all joined again perfectly the inter¬ 
mediate poles will all disappear and there will be only 
the two poles, one at each end. It is, however, possi¬ 
ble to arrange a bar magnet so that it shall have a 
number of poles throughout its length, ev<m while it 
remains solid. This is illustrated in Figure I, where 



Magnetism 


21 


the two ends of the bar are magnetized in opposite 
direction so that two poles of same sign are formed in 
the center and oppose each other. 

Consider now the horse-shoe magnet shown in Fig¬ 
ure 5. If we take a magnet of this kind and sprinkle 
a lot of iron filings or small tacks about the ends they 
will be attracted and form around it in the manner 
shown. If the magnet is weak it will be necessary to 
assist the formation somewhat by gently placing the 
tacks where they will.stick. If we now raise the mag¬ 
net, a large part of the filings or tacks will follow 
and we can carefully put on a number more, but shall 
soon learn that there is a limit and that as we put on 



Figure 4 


more tacks in one place some of the others will fall 
off. If we now take the armature A and place it 
across the pole of the magnet, say at O, by far the 
greater part of the tacks will fall off. The reason for 
this is that the magnetic flow or flux, as it is usually 
termed, follows along the lines of least resistance like 
any other flow. The armature offering a path of 
much lower resistance than the partially disconnected 
tacks simply shunts the flow around them and they 
cease to be attracted. 

The magnetism is conceived to consist of a flow of 
lines of force as indicated in Figure 6. These lines 
are supposed to leave the magnet at the north pole N 








22 


Operating and Testing 


and passing through the intervening space, to return 
to the south pole S of the same magnet. If we take 
a compass and beginning, say at the right hand end, 
move the needle along the path of the lines of force 



Figure 5 


we shall see it align itself to them and as it is brought 
to the other end of the bar the other end of the needle 
will meet it. The flow of these lines of force is greatly 
facilitated by iron or steel but there is no medium 



which can be interposed that will prevent the flow en¬ 
tirely; in other words, there is no insulation for mag¬ 
netism. It is, however, possible to shield bodies from 
it by introducing an easier path for it as we have seen 
in the experiment with the tacks. 











Magnetism 


23 


Permanent magnets are generally made by “ touch¬ 
ing,” that is, a magnet is wiped across the end of the 
bar which is to be magnetized as shown in Figure 7. 
If the inducing magnet is strong it is not even neces¬ 
sary to bring it in contact with the bar to be magnet¬ 
ized. One must proceed in a systematic manner, how¬ 
ever, that is, always touch the same end of the bar to 
be magnetized with the same end of the magnetizing 
bar and move it over the bar in the same direction. If 
this is not done one “touch” will neutralize the other 
and the result will be either no magnetism at all or at 
best but a very little of it. 



Figure 7 


Permanent magnets are often made up of a number 
of bars of equal length and shape fastened together 
and are then known as compound magnets. Perma¬ 
nent magnets can be demagnetized by heating to a red 
heat. 

ELECTRO-MAGNETS 

Electro-magnets differ from permanent magnets; 
first, in being made of soft iron instead of steel; sec¬ 
ond, the magnetizing force is not another magnet, but 
a current of electricity; third, the magnetism lasts only 
while the current is circulating in the wire wound 







24 


Operating and Testing 


around the core; fourth, the strength of magnetism is 
variable and within certain limits in proportion to 
the current flowing; fifth, the polarity, or the direc¬ 
tion of the lines of force changes with the direction of 
the current and can therefore be instantly reversed. 

We may now consider the generation of magnetism 
by means of the electric current. 

If we assume the black circle (Figure 8) to be an 
electrical conductor in which the current is flowing 
in the positive direction (i. e., away from us) that 
conductor will be surrounded by lines of forc^ circling 
about it in the direction of the arrows shown. The 
number of lines of force will be directly in pioportion 



Figure 8 Figure 9 Figure 10 


to the current strength (number of amperes) in the 
circuit. If we reverse the direction of the current the 
lines of force will circulate in the opposite direction. 
If we lay two wires, carrying current in the opposite 
direction, side by side as shown in Figure 9 the lines 
of force will repel each other and tend to separate the 
wires; if, however, these wires be carrying current in 
the same direction the lines of force will act in har¬ 
mony and tend to draw the wires together as in Figure 
10. These lines of force are, of course, only concep¬ 
tions, but they are very natural ones. If wires such 
as those shown be thrust through a piece of paper or 
cardboard at right angles to it and if iron filings be 


Magnetism 


25 


sprinkled on the paper and near the wires, these filings 
will have a tendency to arrange themselves in circles 
around the wires as outlined in the figures. In order 
to properly get such an ouline it will be necessary to 
gently jar the paper several times thus temporarily 
annulling the friction which tends to hold them in 
their place, so that they may more readily align them¬ 
selves to the lines of force surrounding the wire. 

If we now wrap a wire carrying a current of elec¬ 
tricity around a bar of iron as shown in Figure 11 
these lines of force will pass through the iron as de¬ 
picted and we shall have a similar circulation of lines 
of force in this case as was observed in a magnetized 



Figure 11 


bar of steel. Magnetism is also produced by a coil of 
wire wound in this way that contains no iron but the 
magnetic flux will be much less. This is due to the 
fact that the iron offers a much lower resistance to 
the flow of lines of force than does air and hence 
their number is greatly increased. The law that gov¬ 
erns magnetic flux is exactly similar to Ohm’s law 
which governs current flow It is: 

Magneto-motive force 

Magnetic flux — -- 

Magnetic resistance 

The magneto-motive-force is produced by the cur¬ 
rent circulating in the coil of wire and so far as mag- 



26 


Operating and Testing 


netism is concerned it matters not at all whether the 
100 amperes circulate once around the bar or certain 
air space or whether one ampere circulates 100 times. 
The magnetizing force is always proportional to the 
product of the number of turns of wire and the cur¬ 
rent flowing in the wire. This product is generally 
known as the “ampere turns .” 



Figure 12 


The magnetic resistance varies with the material 
used inside of the coil, or helix, as it is often termed. 
It is greatest with air (with exception of a few sub¬ 
stances that need not be considered in practical work) 
and least with well annealed wrought iron. The mag¬ 
netic resistance also decreases as the cross-section of 
the iron increases and, conversely, increases as the 
cross-section of the iron decreases, i. e., the core be- 


























































































Magnetism 


27 


comes smaller. The above is rigidly true only for 
air and approximately only within certain limits for 
iron. The conductivity of iron for lines of force 
has a limit and if we attempt to force too many lines 
of force through a given core a point will soon be 
reached where the iron assists the magnetization only 
to a very small extent and any further increase in the 
strength of that magnet will be little more than in 
the ratio that is possible for air. This is illustrated 
by Figure 12 which shows graphically, by means 
of the curves the relative magnetism produced in dif¬ 
ferent kinds of iron and steel. The highest magnet¬ 
ization is possible with annealed sheet iron, the lowest 
curve shown is for cast iron. The numbers along 
the bottom line indicate the relative ampere-turns or 
magnetizing force and those along the vertical line 
the resulting magnetic flux or magnetism. 

We have seen by Figure 11 how the lines of force 
produced by currents of electricity produce magnet¬ 
ism, either in the surrounding air or in a bar of iron. 
If we now coil another wire about the bar and send 
current through it in the opposite direction, or reverse 
a part of the winding in any coil so that current will 
circulate in the opposite direction we shall neutralize 
the influence of the first coil; that is, the lines of 
force produced by the two windings will oppose each 
other and there will he no magnetism if they are ex¬ 
actly equal to each other. If they are not equal then 
the resulting magnetism will be proportional to the 
difference in strength of the two opposing coils. It 
must not be understood that the number of turns of 
wire, size of wire, and current in the wire must be the 


28 


Operating and Testing 


same, but that the “ampere turns” in me two coils 
must be equal. To find the difference we must sub¬ 
tract the ampere turns in the weaker coil from those 
in the stronger. It is not possible to quite neutralize 
the action of one coil by the action of the other but 
we can come very close to it and the remaining mag¬ 
netism can be detected by the most delicate instru¬ 
ments only. Such a winding is known as “ differen¬ 
tial’ ’ and is made use of in many dynamos, motors, 
arc lamps, measuring instruments, etc. 

We may now briefly consider the forms of magnets 
suitable for different purposes. The attraction of an 



electromagnet for its armature varies as the square 
of the number of lines of force passing through both. 
If then we desire to obtain the greatest traction, we 
must see that we obtain the greatest number of lines 
of force that a given current can produce. For this 
purpose it is necessary to arrange the magnetic cir¬ 
cuit so that it shall have the least possible resistance. 
This we obtain when we make the cross-section of the 
core large enough so that the magnetization need never 
be pushed beyond the nearly straight rise of the curves 
shoAvn in Figure 12. The iron core should also be 
made as short as possible. We must, however, have 
space to place a certain number of turns of wire 










































Magnetism 


29 


around the core and it must be long enough to allow 
this. It need not be a bit longer. We must not, 
however, imagine that very much can be gained by 
crowding the windings together as shown in Figure 
13, for in such a case the outer layers of wire become 
very long and introduce unnecessary resistance into 
the electrical circuit and also, this construction makes 
necessary an unusual length of the yoke. As a gen¬ 
eral rule it will be found advisable to make the thick¬ 
ness of the coil about equal to the thickness of the core; 
to make the yoke just long enough so that the coils 



Figure 14 


will not interfere with each other when they are being 
placed in position and to make the core long enough 
to accommodate the necessary wire. 

In Figure 14 we have shown a cross-section 
through an electromagnet showing the windings sur¬ 
rounding the iron and a general scheme of the lines 
of force existing in such a magnetic circuit. The 
armature is shown out of contact with the magnet and 
there is also indicated a considerable leakage of lines 
of force. If the armature is brought down in contact 
with the core it will have a double effect upon the 












30 


Operating and Testing 


lines of force; first, these lines will be increased in 
number because the resistance of the magnetic cir¬ 
cuit has been lowered; second, because the leakage 
also is very much reduced. Reasoning from these 
facts we can readily see that the best proportions for 
the limbs of a magnet depend somewhat upon the use 
it is to be put to; whether the armature is to work 
close to the core, i. e., if the range of action is to be 
small the tendency to leakage will be small and we can 
let the poles of the magnet come reasonably close to- 





Figure 15 


gether and make the magnet very short, but if the 
range of action is to be long we must separate the 
poles more and make the cores longer so as to lessen 
the tendency to leakage. 

Different arrangements of the magnetic circuit are 
also necessary to provide for different speeds of action. 
The solenoid, Figure 15, has a very long range of 
action, it tends to pull the core C up into the coil but 
this action is, on the whole, very slow and not very 
sensitive to small currents. 













Magnetism 


31 


Figure 16 shows a type of magnet that is very 
sensitive to small currents. The main yoke is a 
compound permanent magnet consisting of a number 
of pieces of magnetized steel fastened together. On 
the ends of these permanent magnets are fastened 
soft iron extensions and on these the magnetizing coils 
are wound. This form of magnet was invented by 
Prof. Hughes for use with a printing telegraph and 
means were provided to bring the armature tight 
against the poles where it would stick, held by the 



Figure 16 


magnetism of the steel bars which also magnetized 
the soft iron ends. It was the function of the elec¬ 
tric current circulating in the coils around the soft 
iron extension to oppose or neutralize this magnetism 
and thus release the armature. In this way the arma¬ 
ture could be very quickly controlled and with very 
small currents. 

For quick action the magnetic circuit should not 
be too good. The cores should be short, the winding 
extra thick upon them and the air gap between the 




















32 


Operating and Testing 


cores and the armature considerable. If the armature 
comes in contact with the cores the demagnetization is 
greatly retarded as this helps increase the hysteresis, 
of which we shall speak later. 

A special form of magnet that is often used is dia- 
grammatically shown in Figure 17. In this form 
of magnet the armature A is continually under the in¬ 
fluence of the permanent magnet M. While current 
is passing through the coils in one direction one of 
the cores will attract the armature and the other will 
repel it. If the current in the coils is now reversed 



the magnetism will also be reversed and the armature 
thrown the other way. The end that before was at¬ 
tracted will now be repelled and the one that before 
was repelled will now be attracted. Under the influ¬ 
ence of an alternating current the armature will move 
in time with the current and cause the bell to ring 
as long as the current flows. This form of magnet is 
also very sensitive and such a bell and all apparatus 
of this kind is known as ‘ ‘ polarized. ’ ’ 

The cores for alternating current magnets require 
to be laminated and thoroughly annealed. A lami¬ 
nated core is made up of a number of thin plates as 






























Magnetism 


33 


in Figure 18. The core is subdivided in this way 
as otherwise currents would be induced in the iron 
and these currents would heat the iron and cause con¬ 
siderable waste of energy. The oxidization on the 
plates introduces sufficient resistance to prevent the 
circulation of such currents. 

There is another source of heating of alternating 
current magnets and this is known as “ hysteresis. ’ ’ 



Every piece of iron has a tendency to retain some of 
its magnetism and this magnetism must, when the 
direction of current is changed, be dispelled. This ef¬ 
fect is small with very good annealed iron but quite 
great with inferior iron or steel. 

There is also assumed to exist a sort of friction be¬ 
tween the molecules of iron of which every bar con¬ 
sists and that, with changes in magnetization these 
molecules are forced to align themselves in a different 
manner j thus if these changes are rapid and continu- 
































34 


Operating and Testing 


ous the friction of the molecules will also cause the 
iron to heat. 

Figure 19 shows the waste of energy due to resid¬ 
ual magnetism of different kinds of iron and steel. 



Figure 19 




Figure 20 


The shaded portion between the two sets of curves 
showing the relative amount of magnetizing energy 
wasted. 

Figure 20 illustrates the molecular friction in an 
iron bar. With each reversal of current the molecules 
are supposed to reverse their positions. 

























































Magnetism 


35 


WINDING OF ELECTROMAGNETS 

"We have seen that currents of electricity circulating 
in the wires wound around an iron core or bar pro¬ 
duce magnetism and it behooves us now to learn the 
most advantageous way of applying such currents so 
as to obtain the greatest amount of magnetism from 
a given current. ^A r e know from Ohm’s law that the 
current increases as the length of the wire in the cir¬ 
cuit decreases. If then, considering a fixed electro¬ 
motive force or E.M.F., we wind more coils around 
a given core, the current becomes steadily less as the 
number of turns increases. At the same time, how¬ 
ever, the effect of what current there is increases be¬ 
cause it circulates around the core oftener. If we 
assume the resistance of the wire around the core to 
be the only one influencing the current we shall ob¬ 
tain the following results. Suppose we have ten turns 
of wire, a resistance of one ohm and a pressure of ten 
volts, this will give us a current of ten amperes and 
consequently a magnetizing force of 100 ampere 
turns. Now double the number of turns, the resist¬ 
ance will be double and consequently the current only 
5 amperes, but twenty times 5 again equals 100. So 
long as we use the same size of wire it will matter not 
a bit how' many turns of wire we take, we shall still be 
able to get the same number of ampere turns from the 
same battery unless, however, the length of the viie 
necessary to make a turn increases very much as it 
will if a large number of layers are wound over each 
other. As the current decreases with more turns, 
while the E.M.F. remains constant throughout, it is 


36 


Operating and Testing 


evident that we are getting our magnetism with less 
and less expenditure of energy as we put on more 
coils. How much energy it is advisable to consume 
in producing a certain flow of magnetism depends on 
circumstances. If power is cheap we can use a few 
turns of wire and a large amount of current, if it is 
dear we shall find it to our advantage to provide more 
windings and thus save energy. 

The determining factor of the winding is, however, 
not alone the amount of energy we are willing to ex¬ 
pend in the coils, but the temperature we are allowed 
to maintain. The magnetism created in any coil in¬ 
creases directly as the current but the heat generated 
increases as the square of the current. If in any coil 
we double the current we double the magnetism and at 
the same time increase the heating four-fold. The 
heating of the wires must therefore never be lost 
sight of. 

Let us examine now how a change in the size of wire 
affects the economy of winding. If we take a coil 
containing say 100 turns of wire and place in the same 
space a wire of half the diameter of that of the first 
coil (neglecting differences that may be caused by va¬ 
riations in the relative thickness of the insulation) 
we shall obtain four times as many turns and the wire 
will have but one fourth of the cross-section of the 
former. Its total resistance will therefore be sixteen 
times as great as that of the old coil and from the 
same voltage it will receive but one sixteenth of the 
current; there will be, however, four times as many 
turns and the magnetizing force will therefore be one 
fourth that of the old coil. As the current is here 


Magnetism 


37 


but one sixteenth of the former the energy expended 
per ampere turn will be but one fourth of the former, 
In this case again we receive from the energy ex¬ 
pended per watt, a much greater amount of magnet¬ 
ism, but in order to get the same total amount we 
must increase the E.M.F. in proportion to the in¬ 
creased resistance divided by the increased number 
of turns, in this case sixteen divided by four. 

We cannot always assume, however, that the coils 
of the magnet are the only resistance in the circuit. 
This would apply very well to the field coils of dy¬ 
namos or the regulating coils of arc lamps, but not at 
all to telegraphy for instance. Here the magnets are 
long distances apart and far from the source of cur¬ 
rent and economy demands the use of small wires and 
these have high resistances. In such cases only a part 
of the energy is expended in the magnet coils. To 
illustrate the most advantageous winding of magnet 
coils for these conditions, let us assume the following 
case. Suppose we have an E.M.F. of 100 volts, a line 
resistance of sixteen ohms and a magnet which is 
wound with 100 turns of wire which just fill out the 
space allotted to the coils and which have a resistance 
of one ohm. This gives us a total resistance of 17 
ohms and with 100 volts we therefore obtain very 
nearly 6 amperes making, 6 times 100 or 600 ampere 
turns. The energy consumed in this case will be about 
600 watts. If we now try a wire of half the diameter 
of the former we shall in the same space have 4 times 
as many turns and each turn having only %th the 
cross-section will have 4 times the resistance, so that 
the total resistance of the coil will be 16 ohms and the 


38 


Operating and 'Testing 


total of line and magnet 32. Our current will now be 
about 3.2 and give us 1280 ampere turns. The en¬ 
ergy (in watts) consumed is now 320. For a third 
trial let us again take a wire of half the diameter of 
the former. The number of turns will now be 1600 
and the resistance of the coil 256 ohms, giving us a 
total resistance of 272 and a current of about .4 am¬ 
peres and a total of 640 ampere turns. The energy 
consumed in this case will be only 40 watts. Similar 
results will be obtained with all variations in diameter 
of wire and an inspection of these results will illus¬ 
trate to us the rule, by which most designers of mag¬ 
nets for such work are guided, which is: make the 
resistance of the magnet coils in the circuit equal to 
the resistance of the line. If there are many magnets 
their combined resistance is made equal to that of the 
line. It must be understood of course that only cop¬ 
per wire of the highest conductivity should be used. 


CHAPTER IV 


PRINCIPLES OF DYNAMO-ELECTRIC MACHINES 

The dynamo consists of two main parts, one of 
which is a huge electro-magnet, in the simpler forms 
approximating closely in shape to the horse-shoe mag¬ 
nets with which we are familiar. This magnet in the 



Figure 21 

dynamo is known as the “held magnet” and is often 
spoken of merely as “the fields.” In the simpler 
forms of generator these fields are usually stationary. 

The other part of the dynamo is known as the arma¬ 
ture. In all machines in which the fields are station- 


39 




















40 


Operating and Testing 


ary the armature is made to revolve. In Figure 21 
the fields of the dynamo are designated by the letter 
M and the armature by the letter A. Upon the iron 
<core of the fields are always wound a number of turns 
of wire as upon any electro-magnet, and in this wire 
currents of electricity circulate, producing lines of 
force, just as in the different types of electro-magnets 
we have discussed in the previous chapter. 

In the dynamo the electro-motive-force is developed 
by “cutting” lines of force. Lines of force are said 
to be “cut” when a conductor of electricity is moved 
in a magnetic field in a direction at right angles to 
the lines as indicated in Figure 22. Such a field is 
shown in Figure 22 between S and N and if the bar 
be moved through this field at right angles to the lines 
of force an E.M.F. proportional to the number of lines 
of force cut per second will be generated. No current 
will be generated in the bar as shown as it does not 
form an electrical circuit; but the fact that an E.M.F. 
exists could be readily shown by connecting a volt¬ 
meter across the ends of the bar. The direction of the 
flow of current generated depends upon the direction 
in which the lines of force are cut. By reversing the 
direction of motion of the bar, or by reversing the di¬ 
rection of the lines of force, i. e., reversing the current 
which produces them, the direction of the flow of cur¬ 
rent in the bar will be reversed. 

The direction of the flow of current induced in any 
moving conductor may be determined by the following 
method: Place the thumb and first two fingers of the 
right hand in such a position that each forms a right 
angle with the others as shown in Figure 23. If the 


Principles of Dynamo-Electric Machines 41 

thumb points in the direction of motion of the moving 
wire and the first finger in the direction of the lines 
of force, or from the north to the south pole of the 
magnet, the third finger will point in the direction of 
the flow-of the induced current. 

If the bar in Figure 22 is moved slowly the E.M.F. 
generated will be but small. If the number of lines 
of force remains constant, the E.M.F. will be directly 
proportional to the speed with which the bar is moved. 
If the speed of the bar remains constant the E.M.F, 



will vary directly as the lines of force vary. We can 
therefore raise or lower the E.M.F. of any dynamo by 
varying either the speed ^of the moving conductors or 
the intensity of the magnetization of the fields or by 
both. 

An E.M.F. of one volt is obtained for every 100,- 
000,000 lines of force cut per second. If therefore 
the gap in the iron of the fields has a cross-section of 
100 square inches, and the magnetization is equal to 
20,000 lines per inch, the bar would have to cut 





















42 


Operating and Testing 


through this field 50 times per second to generate an 
E.M.F. of one volt. 

The generation of E.M.F. in this way is known as 
electro-magnetic induction. 

Figure 24 represents a coil of wire the .ends of 
which are connected to the two collector rings 1 and 
2. Brushes bearing upon these collector rings con¬ 
nect the coil to the external circuit C. If now this 
coil of wire were revolved around an axis indicated 
by the dotted line through the center of it and in the 



magnetic field, it would generate a current which 
would manifest itself in the outer wires C, either by 
heating them or by its effect upon instruments we 
may place in the circuit. We can get a clearer idea 
of the nature of this current and the laws governing 
it by reference to Figure 25 which shows an end view 
of the same coil of wire. 

Let the points 1 l 1 represent opposite sides of the 
coil and let them revolve at a uniform rate of speed; 
they will then successively move to the points 2 2 1 ; 
3 3 1 ; 4 4 1 until l 1 is at the point now occupied by 





















Principles of Dynamo-Electric Machines 43 

1. The wires will in this time have made one half 
revolution. We have seen that the E.M.F. generated 
is proportional to the rate of cutting lines of force. 
We can see by an inspection of Figure 25 that the 
rate of cutting lines of force is not uniform, for at 1, 
for an instant the wire is moving practically parallel 



to them and is not cutting any. Also during Vs °f 
one revolution from 1 to 2 it is not cutting nearly as 
many lines as during the time it travels from 2 to 3. 
In fact while the wires are at the exact points 1 l 1 , no 
E.M.F. is generated, but as they pass this point it 
begins gradually to rise until 1 is at 3 when it begins 



gradually to fall until 1 is at l 1 when it is again at 
zero. When 1 has passed the point now occupied by 
l 1 the E.M.F. again begins to rise but in the opposite 
direction, for the lines of force are now being cut in 
the opposite direction. The rise and fall of E.M.F. 
or current in an armature coil operating in this man- 








44 


Operating and Testing 


ner can be illustrated by mean of “curves’ 7 as shown 
in Figure 26. Everything above the neutral line N 
being taken as representing E.M.F. in one direction 
and everything below as in the opposite direction. 
These curves show us also that the currents actually 
generated in a dynamo-electric-machine are alternat¬ 
ing in direction and variable in strength. Alternat¬ 
ing currents are not, however, always desirable and 
it becomes necessary to rectify them so as to obtain 
continuous or direct currents. For this purpose a 
commutator is provided. 




The nature and general construction of the commu¬ 
tator can be seen from Figure 27. It consists in these 
simple cases of two sections of copper connected to 
the terminals of the coils arranged as an armature. 
If the coil equipped with such a commutator is now 
revolved, it will be seen that just at the time when the 
open section of the commutator is in line with the 
dotted line in either one of the figures, the brushes 
B, which bear upon the commutator and connect it 
with the exterior circuit are in a position to change 























Principles of Dynamo-Electric Machines 45 

from one section to the other. If the brushes are prop¬ 
erly set this will occur at the precise moment when 
the coil is at the point where it is generating no cur¬ 
rent as in Figure 27. This is the point at which the 
current in the armature (coil of wire between the pole 
pieces) changes in direction. 

The current in the armature continues to alternate, 
i.e., change in direction, at every half revolution, but 
by means of the commutator the coils are disconnected 
from one side of the external circuit and connected 
to the other so that the current in the exterior circuit 
remains always in the same direction. The E.M.F. 
or current generated by an armature containing only 



Figure 29 


one or a few turns of wire like the one shown would 
still produce a pulsating current and this current 
would be represented by such curves as are shown in 
Figure 29. These currents are all in one direction 
but vary in strength from zero to the maximum of 
which the machine is capable. 

It will be noticed that the brushes, during the mo¬ 
ment they are changing from one commutator seg¬ 
ment to the other, are in contact with both of them. 
It could of course be arranged to avoid this by mak¬ 
ing the brushes narrow and the space or insulated 
material between the two segments wide so that the 
brushes would leave one section before they came in 
contact with the other. This would, however, cause 



46 


Operating and Testing 


an opening of the circuit every time the armature 
made a half revolution and would result in very un¬ 
satisfactory lighting and motor service besides caus¬ 
ing very annoying and destructive sparking, as every 
break in an electric circuit is accompanied by an arc 
which rapidly eats away copper and insulating ma¬ 
terial. The brushes connecting together the two seg¬ 
ments, it will be seen b}^ inspection of Figure 27, cause 
the coil to be on short circuit during the time that the 
brush is in contact with both of them. If this hap¬ 
pens while the coil is in a position where it is not gen¬ 
erating any E.M.F. and consequently no current is 
flowing no harm will be done; but if this occurs at a 
time when the coil is in an active part of the field 
and generating, a very considerable current will be 
produced because the resistance of such a coil is 
usually very low. This current will heat the wire 
and cause considerable waste of energy,—energy that 
should appear in the external circuit, but now does 
no useful work. Aside from this waste of energy and 
troublesome heating of the armature, when the brush 
breaks contact with one of the segments, this current 
will be broken and manifest itself in the form of a 
spark which, recurring often, will quickly destroy the 
commutator. 

Not only this, but the commutator, if the position 
of the brushes is very wrong, as in Figure 28, would 
fail of its purpose and not rectify the current at all. 
"With a single coil and the brushes set as in Figure 28 
the current would be graphically represented by 
curves such as shown in Figure 30, it would still be 
an alternating current changing in direction in an 


Principles of Dynamo-Electric Machines 47 

irregular way. In practice armatures do not consist 
of a single coil and only in very exceptional cases 
would these considerations in the extreme form apply. 
The commercial armature has a greater number of 
turns of wire and for bipolar, or the simpler machines, 



Figure 30 


is made up either as shown in Figure 31 or diagram- 
matically in Figure 32 which is known as the gramme 
ring type of armature, or as shown in Figures 33 and 
34 which is known as the “drum” armature. 



By reference to Figure 32 we can continue our 
study of the armature in. a more commercial form. By 
noting the position of the brush B we can see that it 
is about to short circuit the coil connected to the two 

















48 


Operating and Testing 


segments to which it is nearest. This coil is, however, 
only a small part of the whole and a wrong placing 
of the brushes would not have the effect outlined be¬ 
fore in regard to armatures having but one coil. No 
matter how the brushes may be set, they short circuit 
only one coil each and therefore only a small part of 
the current is ever broken or changed in direction at 
one time. As the resistance of such a coil is, however, 



very low the current generated in it is, if it is in an 
active part of the field at the time, quite sufficient to 
cause trouble, which usually indicates itself by more 
or less severe sparking. If the coil is located in the 
neutral part of the field as that of Figure 32, for in¬ 
stance, there will be no sparking. The smaller each 
individual coil is made the easier it becomes to realize 
this condition and for this reason dynamo armatures 
are generally made up of a large number of coils, and 
















Principles of Dynamo-Electric Machines 49 

of course a corresponding large number of commuta¬ 
tor segments. 

The position of the brushes also has a great deal to 
do with the E.M.F. generated by the dynamo. To 
comprehend this let us again refer to Figure 32. The 
lines of force are passing through the fields and ar¬ 
mature in a certain direction, from N to S. We know 
that the direction of the current depends upon the 
direction in which these lines are cut by the wires. 
As the armature is revolving always in the same direc¬ 
tion those lines at S are cut in an opposite direction 



Figure 33 

from those at N, consequently the currents generated 
in the two halves of the armature are flowing in a di¬ 
rection towards each other; this causes them to meet 
at the positive brush, flow out through the circuit and 
return to the negative brush, dividing again in the 
armature. In this way it can readily be seen that 
the two halves of the armature are in parallel. Now 
let us move the brush one section forward. Before, we 
had two coils in the neutral part of the field, generat¬ 
ing no current, and three coils under the influence of 
each field doing active work. Now we have still two 
coils in the neutral field, idle, and the currents in each 




















50 


Operating and Testing 


direction are generated by two coils under the influ¬ 
ence of each field and one under the influence of the 
the other; but this latter coil is not generating in har¬ 
mony with the other two, it is actually opposing them 
as it is under the influence of the opposite field. This 
position of the brushes is therefore not only the cause 
of much sparking but also reduces the voltage of the 
dynamo. By shifting the brushes, forward or back, 


I 



*t~ 


Figure 34 

until they are at right angles to the neutral line the 
voltage can be reduced to zero. If the brushes are 
shifted still farther the voltage will again begin to 
rise but in the external circuit current will be in the 
opposite direction. 

In present day practice the brushes are used to reg¬ 
ulate the voltage of dynamos only in exceptional cases 
which will be considered in another chapter. The 









Principles of Dynamo-Electric Machines 51 

necessary regulation is almost invariably brought 
about by means of a variable resistance or ‘ ‘ rheostat. ’ ’ 
Such a rheostat is cut into the field circuit of a dy¬ 
namo as shown in Figure 35 which shows a diagram 
of a simple shunt dynamo, A being the armature, F 
the field wires, R the rheostat and L the exterior or 
lead wires of the dynamo. When the machine is in 
operation current circulates around the fields and 
through the wires of R. The arm of R is a conductor 



and is movable. In the position shown the current 
in the wires must traverse the greater part of the 
wires in R. If the arm of R, however, is moved to 
the left it gradually cuts out coil after coil until when 
it arrives at the last notch all of the resistance of R is 
out of the circuit. The resistance of the circuit is 
then at its lowest and consequently the current at 
its highest value and the field the strongest. By mov¬ 
ing the arm in the opposite direction we cut more re- 









52 


Operating and Testing 


sistance into the circuit and thus weaken the fields of 
the dynamo. 

By moving the bar in the proper direction we can 
therefore increase or decrease the current strength in 
the fields and thus change the number of lines of force 
in the armature and these in turn (speed of armature 
remaining unchanged) will govern the E.M.F. of the 
generator. 

The current flowing in the external circuit depends 
upon the E.M.F. and the resistance in the circuit. 
The current is all generated in the armature and of 



Figure 36 Figure 37 

course all passes through it. And this current also 
makes a magnet out of the armature and the resulting 
magnetism opposes the magnetism of the fields to a 
certain extent as we shall see by reference to Figure 
36. We can determine the direction of current in an 
armature by the following rule which has already been 
given but is repeated here for convenience of the stu¬ 
dent. Grasp the north pole of the dynamo with the 
right hand arranged as in Figure 23. Let the index 
finger point in the direction of the lines of force and 
the thumb in the direction of motion; the middle fin- 












Principles of Dynamo-Electric Machines 53 

ger will then point in the direction the current is said 
to be flowing. With condition as shown in Figure 
36 the current will be flowing around the armature as 
indicated by arrow points. Current flowing in this 
direction will produce lines of force in the armature 
as indicated by the other arrow points. It will be 
noted that these lines of force oppose those coming 
from the N pole to a certain extent. As lines of force 
can never intersect each other the result of this op¬ 
position is that the lines of force which pass through 
the armature and induce poles in it as shown in Fig¬ 
ure 37 while no current is flowing in the armature, are 
deflected to a certain extent as shown in Figure 36. 

Figure 36 shows the counter-magnetization of the 
armature which results in deflecting the lines of force 
from the fields somewhat in the direction of motion of 
the armature. In actual practice the lines of force 
from the fields reverse those of the armature but are 
deflected by them and the general trend of the result¬ 
ant lines of force is indicated by the curved line F, 
Figure 36. 

The neutral point or point at which the brushes 
must be set for least sparking is therefore no longer 
in the center between the two pole pieces as in Figure 
37, but is shifted somewhat in the direction of motion 
of the armature as in Figure 36. If we reverse any 
one of the conditions the current will be reversed but 
the same relation between shifting of the neutral point 
and direction of motion will always hold. The coun¬ 
termagnetization of the armature increases as the cur¬ 
rent increases and therefore it becomes necessary to 
shift the brushes in the direction of motion as the load 


54 


Operating and Testing 


increases and in the opposite direction as the load 

decreases. 

It is evident that this shifting of the brushes which 
becomes necessary when the current flow in the dynamo 
changes, depends almost entirely upon the relative 
strength magnetically of the fields and armature. If 
the machine is so constructed that the magnetism of the 
armature is very strong, then, as the current increases 
the magnetism will increase and greatly shift the neu¬ 
tral line and make necessary considerable shifting of 
the brushes. But if the fields are very strong com¬ 
pared to the armature the latter will have but little 
effect and but a very little shifting of the brushes will 
be necessary. 

In connection with dynamos two terms are often 
used erroneously as having the same meaning. These 
terms are electro-motive force or E.M.F. and differ¬ 
ence of potential or P.D. for short. Strictly speaking, 
the term E.M.F. refers only to the greatest difference 
of potential the machine or battery can produce and 
this P.D. can exist only while an infinitesimally small 
current is flowing. Whenever any appreciable cur¬ 
rent is flowing there is always a loss of potential 
which is always equal to IXR- To get the maximum 
voltage of a dynamo we must therefore arrange that 
no current except that through the voltmeter be flow¬ 
ing. In a poorly constructed armature the difference 
between E.M.F. and difference of potential is consid¬ 
erable. 

Aside from the foregoing there are many other 
points about dynamos that require explanation but 
these can more readily be treated in connection with 


Principles of Dynamo-Electric Machines 55 

the particular type of machine in which they are of 
greatest importance. 

In general a good dynamo has a large number of 
commutator sections. (To avoid sparking.) A mag¬ 
netically weak armature and strong fields. (To avoid 
shifting of brushes.) The fields are wound with many 
turns of fine wire. (To save energy. See chapter on 
magnetism.) A small air gap between fields and ar¬ 
mature. (To prevent leakage and unnecessary mag¬ 
netic resistance.) The ends of pole pieces not too 
close together. (To prevent leakage around arma¬ 
ture.) Large wires on armature. (To prevent loss 
of voltage and heating.) 


CHAPTER V 


TYPES OF DYNAMOS 

The oldest type of dynamo is shown diagrammat- 
ically in Figure 38. The use of this type is generally 
restricted to direct current arc lighting. It is known 



as the series dynamo, the same current passing in se¬ 
ries, first through the armature, then through the 
fields. Such a machine cannot be used with a vari¬ 
able current because the strength of the fields, would 
be constantly fluctuating. Whenever there would be 
an increase of current strength there would also be 
an increase in voltage and with a decrease in current 
strength there would be a drop in voltage. As the po¬ 
tential of series arc circuits is generally very high, 


56 














































Types of Dynamos 


57 


sliunt wound dynamos would require a great length 
of very fine wire and consequently would be very 
expensive and also very likely to be damaged. This 
is one reason why series dynamos are in special favor 
in connection with series arc circuits. 

The regulation of this type of dynamo always has 
as its object the raising of the E.M.F. as more lights 
are cut into the circuit and a corresponding lowering 
of it as lights are cut out of the circuit, so that the 



E.M.F. is always at its proper value in regard to the 
resistance of the circuit to cause the necessary current 
to flow. This regulation is generally brought about 
in one of the following ways: By shifting of the 
brushes, by commutation of the fields, or by a com¬ 
bination of these two methods. 

The method employed of shifting the brushes au¬ 
tomatically is diagrammatically illustrated in Figure 

























58 


Operating and Testing 


39. The total dynamo current passes from the posi¬ 
tive pole of the armature A to the lamps, thence to 
field F, solenoid S and negative pole of dynamo. We 
know that the solenoid has power to control the po¬ 
sition of the core within it. The stronger the current 
the farther will the core be pulled in in opposition to 
the supporting spring. This core is so arranged that 
with the normal current strength the extension 1 rests 
about midway between the points 2 and 3. If now 
there is a slight increase in current strength, as when 
a lamp is switched out, the core will be drawn down¬ 
ward and close an electric circuit at 2. This circuit 
is a shunt to the solenoid and requires but a small cur¬ 
rent. When it is closed current passes through the 
clutch 4 and this (by a mechanical contrivance not 
shown) causes the yoke Y to be drawn over so that the 
brushes are shifted in the direction which causes a 
lowering of the voltage and a decrease in current 
strength. As soon as the current goes back to its 
normal strength the circuit at 2 is again open and the 
brushes remain at rest until another change in current 
strength causes the solenoid to change its position. If 
the current becomes too weak the spring draws the 
solenoid up until the circuit at 3 is closed and the 
brushes shifted in the opposite direction by means of 
clutch 5. 

The principle of varying the E.M.F. by field com¬ 
mutation is illustrated in Figure 40. The automatic 
control is not shown and instead hand control is used. 
By moving the lever L to the right or left more or 
less of the field winding can be cut into the circuit. 

Instead of cutting: out field coils, a resistance R (see 


Types of Dynamos 


59 


Figure 41) is sometimes arranged as a shunt around 
the field coils and as the arm is moved forward or 
back the resistance is increased or decreased, thus tak¬ 
ing more or less current around the fields and weaken¬ 
ing or strengthening them accordingly. 

The highest E.M.F. of which the dynamo is capable 
is obtained when the brushes are near the neutral 
point. This position of the brushes can only obtain 
when the maximum number of lights are in the cir¬ 
cuit. With a lesser number of lights the brushes must 



be shifted away from the neutral point sufficient to 
cause a certain number of the armature coils to gener¬ 
ate in opposition to the rest and thus reduce the 
E.M.F. of the dynamo until the current has its pre¬ 
determined value. 

From what we have learned in chapter on Principles 
of Dynamos it is evident that all dynamos subject to 
such regulation must spark considerably at the 
brushes. There must also be considerable tendency 













60 


Operating and Testing 


toward heating of armature wire with this kind of 
regulation as some of the coils are nearly always on 
short circuit. This applies also to a great extent to 
machines regulated by field commutation. Machines 
of this type are in consequence usually equipped with 
some special form of commutator calculated to with¬ 
stand the destructive effects of the arcs formed. In 
the Thomson-Houston dynamo a blower is provided 
which blows out the arc. 

For dynamos of this type the Gramme ring arma¬ 
ture is preferable because from the nature of its wind¬ 



ing wires of opposite polarity do not cross each other 
as they do in drum armatures. 

Two special types of dynamos very generally used 
for series arc lighting are the Brush and Thomson- 
Houston. 

Figure 42 shows the coils and commutator sections 
of an 8 coil Brush arc dvnamo. The diametricallv 
opposite coils 1-1; 2-2, etc., are connected in series and 
each coil has its own exclusive commutator section. 















Types of Dynamos 


61 


By tracing out the circuit from the brush A, it will 
be seen that current enters at this brush, passes 
through coil 1-1 to brush A 1 ; thence to field H, brush 
B, coils 2 and 4 in parallel, thence to brush B 1 and out 
at the positive pole of the dynamo. 

With this armature one coil is always on open cir¬ 
cuit and the adjustment must be such that this coil 
while open is in the dead part of the field. Each com¬ 
mutator segment embraces three eighths of a circle. 



As the different coils are not in series with each 
ather but at times in parallel the brushes must be so 
arranged that at no time can a coil that is not gen¬ 
erating be left in circuit. Such a coil would simply 
form a short circuit to the line and much of the cur¬ 
rent that should flow through the line would flow 
through it. By following out in imagination a com¬ 
plete revolution of the armature one can see that the 
brushes always break contact with the coils as they pass 





























Operating and Testing 


62 

out of the influence of the fields. It is very import¬ 
ant to see that the commutator is always set with re¬ 
gard to this. 

The Thomson-Houston is another type of open cir¬ 
cuit dynamo armature. The nature of its winding is 
shown in Figure 43. One end of each coil is con¬ 
nected to one of the 3 commutator sections and the 
other to a brass ring R common to all the coils. 

A series dynamo if left without regulation will, with 
an increase of current, run its E.M.F. to the maxi- 



Figure 43 

mum of which it may be capable and probably bum 
out. The greater the current the greater will be the 
pressure, but after the fields have become fully sat¬ 
urated the increase in E.M.F. will be small. Figure 
44 shows the characteristic curve of such dynamos. 
Such curves are obtained by plotting the E.M.F. and 
current existing at the same time on squared paper as 
shown and then combining the points so obtained in a 
curve. This may be to any convenient scale. The 
figure shows only the general outline of such curves 








Types of Dynamos 


63 


as they are of course different with different types and 
design. 

For incandescent lighting, motor service, constant 
potential arc lighting and storage battery work the 
shunt dynamo is much used although of late years the 



Figure 44 

compound wound dynamo is crowding it out. Figure 
45 is a diagram of the shunt dynamo. This dynamo is 
generally equipped with a drum armature. It is sel¬ 



dom if ever equipped with an automatic regulator and 
instead hand regulation is used. The drop of poten¬ 
tial at the brushes is equal to the current multiplied 
by the resistance of the armature. In a poorly con- 































































































64 


Operating and Testing 


structed armature this is considerable so that such a 
machine needs constant watching. An appreciable 
drop in potential is of course accompanied by a weak¬ 
ened current through the fields which in turn allows 
a further falling off in potential. 

The characteristic curve of a shunt dynamo is given 
in Figure 46. If the potential of such a dynamo falls 
off noticeably the fields begin to weaken and thus in¬ 
crease the falling off in proportion. A shunt dynamo 
if short circuited will for a very short time increase its 
current enormously and will then lose its pressure, the 
short circuit robbing the fields of all current. The 



Figure 46 

curve in Figure 46 shows the effect of an overload 
which is nearly or fully equivalent to a short circuit. 
After the maximum current has been reached the 
pressure falls off so much that the current also de¬ 
creases and both current and E.M.F. finally return 
to 0. 

As all armatures have some resistance it follows 
that the potential at the brushes of any shunt dynamo 
must fall as the current increases. To compensate for 
this a special winding through which the whole dy¬ 
namo current flows is put upon the fields in addition 
to the shunt winding. As the drop in potential is 






















































Types of Dynamos 


65 


always exactly in proportion to the current flowing, 
it is evident that if this current be made to circulate 
the proper number of times around the fields it will 
increase their strength so that the E.M.F. of the dy¬ 
namo will be raised just enough to make up for the 
loss due to its armature resistance and the E.M.F. 
remain very nearly constant. (See Figure 47.) If 
the current be made to circulate a greater number of 
times the E.M.F. of the armature will go higher 
as the current increases. It is therefore possible to 



arrange such dynamos to keep the pressure constant 
even at points far away from the machine, but in 
such cases it will go undesirably high at the dynamo 
terminals. 

The characteristic curve of a compound wound dy¬ 
namo is a combination of the curves of a series and 
shunt machine and shown in Figure 48. If such a 
dynamo is short circuited the shunt fields will im¬ 
mediately lose their magnetism but the power of the 
series coils will be momentarily increased as there will 















































66 


Operating and Testing 


be for a very short time a great flow of current, due 
to the fact that an instant of time is necessary before 
the magnetism of the fields passes away. If the series 
fields are very strong compared to their own and the 
armature resistance they will energize the fields on 
their own account and the armature will burn out. If 
it is very weak relatively to those two factors, little 
harm will be done if the armature has withstood the 
momentary rush of current which could last only long 
enough for the shunt fields to die down. 

So far we have looked upon all machines as having 
but two poles. Such machines are known as bi-polar. 



Figure 48 

Most of the larger machines are, however, multipolar, 
i. e., equipped with more than two poles. The mag¬ 
netic circuits and arrangement of pole pieces in a 4 
pole machine are shown in Figure 49. With such ma¬ 
chines there is usually a set of brushes for each set of 
poles. The neutral point will be about midway be¬ 
tween two pole pieces. If the brushes are moved a 
quarter revolution forward or back the directions of 
current will be reversed. Armatures for such ma¬ 
chines may be wound just as for bi-polar fields but a 
form of winding as indicated in Figure 50 is prefer¬ 
able. 


























































Types of Dynamos 


67 


Figure 50 is a diagrammatic view of the simplest 
form of multipolar armature winding. The wires are 
laid in slots on the outer circumference of the arma¬ 
ture and are shown as though the armature were cut 



in two and the wires laid out flat. "W, "W represents 
the commutator sections and N, S, the poles as in 
Figure 49. 



A view of a finished armature is given in Figure 51. 
Alternating currents to be available for lighting 
purposes must have quite a high frequency; 60 cycles 










































68 


Operating and Testing 


per second or 7200 alternations per minute being 
about the lowest frequency that can be used for arc 
or incandescent lighting without causing annoyances 
through bickerings in light. If such frequencies were 
to be produced by a bi-polar machine it would have to 
operate at a speed of 3600 revolutions per minute. As 
these machines also generally operate at very high 
pressure there would also be, with drum armatures, 
great danger from wires between which great differ¬ 
ence of potential exists crossing each other. To ob¬ 
viate the above troubles alternators are usually made 



Figure 51 


multipolar, both, fields as well as armature, consisting 
of a number of sections. 

The alternating current dynamo may have its ar¬ 
mature stationary and the fields revolving; it may 
have the fields stationary and the armature revolving 
or the fields and armature may both be stationary. 
In the latter case it is described as belonging to the 
inductor type. 

An alternating current cannot be used as such to 
excite the field and consequently many dynamos are 




Types of Dynamos 


69 


separately excited by an outside dynamo. Some al¬ 
ternators, however, are provided with commutators 
which rectify the current and make it available. 

Figure 52 shows the general layout of an alternat¬ 
ing current dynamo with revolving fields and sta¬ 
tionary armature. The dynamo is excited by direct 
current from a shunt dynamo, the current entering at 
D.C. and passing around the fields. The strength of 



this current can be regulated and through it the E.M.F. 
of the dynamo. 

Every time one of the armature poles passes from 
under one of the stationary poles to the next one there 
is a reversal in direction of the current. 

If supplying a variable load the E.M.F. of the dy¬ 
namo will be constantly fluctuating, the drop increas- 














































70 


Operating and Testing 


ing as the load increases and with this machine there 
is only hand regulation. 

In order to avoid the necessity of constant attend¬ 
ance and hand regulation alternators are sometimes 
compound wound just as direct current machines. 
The field of such a machine consists of a steady current 
from the D.C. dynamo supplemented hy a pulsating 
current from the generator itself. 

In order that the generator current may be used it 



must be rectified so that, although it is variable in 
strength, the pulsations all pass through the fields in 
the same direction. For this purpose the rectifier R, 
Figure 53, is provided. This rectifier is fastened to 
the same shaft as the armature and revolves with it. 
All of the white sections of R are joined together by 
the. wires shown as forming a square and the shaded 
by the wires shown as curved lines. The shaded sec- 



















Types of Dynamos 


71 


tions connect direct to collector ring 2 and the white to 
the wire coming from the armature, as shown. The 
brushes shown bearing upon the rectifier are adjusta¬ 
ble and are to be set so that at the moment when the al¬ 
ternating current is passing through the zero part of 
its waves, the connections are changed, i. e., one brush 
changes from a shaded segment to a clear one and the 
other vice versa. By this arrangement the current 
passing through the fields of the generator (stationary 
in this case) remains always in the same direction al¬ 
though that in the line is alternating. The main cur¬ 
rent can readily be traced, beginning at A, collector 
ring 1, armature, clear sections of rectifier, fields, 
shaded portion of R to collector ring 2 and the line, 
finally returning to A. The direct current field circuit 
is shown at D C. 

The rectifying arrangement works quite satisfacto¬ 
rily as long as the load is of constant inductance. 
This is, however, only the case so long as merely in¬ 
candescent lights are in circuit. When motors o? arc 
lights are operated the current does not always co¬ 
incide in phase with the normal adjustment of arma¬ 
ture and rectifier and begins either to lag or lead, that 
is, the zero part of the wave occurs a little later or 
earlier and therefore the change of rectifier segments 
is made at a time when there is considerable current 
flowing, which results in severe sparking unless the 
brushes are constantly being shifted. For this rea¬ 
son the rectifier is not being much used at present. 

It will be seen that by shifting the brushes the full 
width of a segment the direction of the current around 
the fields can be reversed. A variable shunt S can be 


72 


Operating and Testing 


arranged by means of which more or less of the rec¬ 
tified current can be diverted from the field circuit. 

In actual practice the generating coils of alterna¬ 
tors are not wound upon projecting coils but laid into 
slots as indicated in Figure 54. Sometimes each slot 
contains only one wire; sometimes there are many. 
The number of slots per pole also varies. For two 
and three phase machines two or three windings are 
arranged either upon the rotating or stationary part. 
In Figure 54 there are three slots per pole and this 
armature is designed for three phase currents. The 



Figure 54 


positions of the wires for one of the phases is indi¬ 
cated by the black circles. As these sweep around 
under the pole pieces the currents induced in each 
wire are in a different direction and to make all of 
them generate in series they are connected on the two 
sides of the armature as shown by the heavy black 
lines, where the arrows indicate direction of induced 
currents. The other two phases are wound into the 
empty slots in the same manner, and it can be seen 
that while the phase represented by the black circles 









Types of Dynamos 


73 


is at a maximum, being directly in the strongest part 
of the field, that at the right of it is increasing and the 
one at the left decreasing. These wires are connected 
to collector rings in such a manner that in the outside 
circuit they are in opposite directions, one wire al¬ 
ways forming the return for the other two. A partial 
diagram of the winding is shown in the center of the 
figure. 


CHAPTER VI 


PRINCIPLES OF ELECTRIC MOTORS—DIRECT CURRENT 

The reader will, no doubt, have noticed that there 
is no great difference between a dynamo and a motor 
and that there are about as many different types of 
one as of the other. As a matter of fact, any dy¬ 
namo can be used as a motor and any motor as a 
dynamo, although as a rule less care is bestowed upon 
the manufacture of motors and most of them would 
operate at very low efficiency if installed as generators. 

In the shunt dynamo we apply power to revolve the 
armature in the fields and the power required is pro¬ 
portional to the current flowing. If the armature is 
on open circuit we require no more power than is 
necessary to overcome the friction. It is, therefore, 
the reaction of the current in the armature against 
the fields which requires the power to overcome it. 
It follows from this that if we take the belt from a 
dynamo and arrange for an equal current from some 
other source to flow through the armature in the same 
direction we must obtain motion, but in a direction 
opposite tO' that in which the armature was revolved 
when generating. 

Let us look at this a little more in detail. Figure 
55 shows the armature and fields of a motor. Cur- 


74 


Principles of Electric Motors—Direct Current 75 

rent is flowing into the armature through the brushes. 
We have seen that the two halves of such an armature 
are in parallel and that the current magnetizes the 
armature, setting up poles as indicated by N and S. 
Arranged as shown in the figure, the S pole of the 
fields will attract the N pole of the armature and repel 
the S pole. This will cause the armature to move to 
the right and were it not for the commutator it would 
move only until the poles of armature and fields 
had aligned themselves. But as the armature moves 
the brushes change connections coil by coil and the 



S 


Figure 55 

N and S poles of the armature remain always in th& 
same position, thus keeping the armature always in 
motion in a vain endeavor to align itself and come to 
rest. Should we change direction of current either in 
field or armature, the motion would be in the opposite 
direction. If current through both fields and arma¬ 
ture is reversed motion will continue in the same di¬ 
rection. The pull of the armature is governed by the 
current flowing in it and the strength of the fields. 

Since the motor is the exact counterpart of a dy- 











76 


Operating and Testing 


namo and its armature operates in a field precisely 
similar to that of a dynamo, it follows further that it 
must generate an E.M.F. just like a dynamo, and so 
it does, and this E.M.F. is always opposed to that of 
the dynamo from which the motor receives its cur¬ 
rent. This E.M.F. is known as the “counter E.M.F .’ 9 
of the motor and varies with the strength of field and 
speed of armature, or, in short, with the rate of cut¬ 
ting lines of force just as the E.M.F. of the dynamo 
does. The current which flows from the dynamo to 
the motor varies as the difference between the E.M.F. 
of the dynamo and the counter E.M.F. of the motor. 
Thus, if the voltage of the dynamo be 110 and the 
counter E.M.F. of the motor 105, the current flow 
through the motor will be due only to the five volts. 
The torque or pull of a shunt motor will depend upon 
the current, and consequently as a greater load comes 

on the motor, it must slow up until its counter E.M.F. 

• 

is sufficiently reduced to allow the requisite current 
to flow. 

If the armature of a motor have a very high resist¬ 
ance, it follows that its counter E.M.F. must be much 
lower than the E.M.F. of the dynamo in order that 
the necessary current may be forced through it. If 
with such an armature an additional load is thrown 
on, it must, of course, slack off in speed considerably 
in order to lower its counter E.M.F. sufficiently to 
draw the necessary current. The lower the resistance 
of the armature, therefore, the nearer constant the 
speed of the motor. This applies also to the resistance 
of the line. This fact is often made use of in regu¬ 
lating the speed of motors, an artificial, variable re<- 


Principles of Electric Motors—Direct Current 77 


sistance, known as a rheostat being cut into the circuit 
to control the speed. 

So long as the motor is at rest, it has of course no 
counter E.M.F. If, at such a time the dynamo cur¬ 
rent were turned on, the armature of the motor would, 
up to the time that it acquired its proper speed and 
developed a counter E.M.F., present a circuit of very 
low resistance and be subject to an enormous current 
flow, which would speedily cause it to burn out. To 
prevent this a rheostat is always cut into the arma- 



Figure 56 

ture circuit. Figure 56 shows diagrammatically the 
circuits of a simple shunt motor. When the motor is 
to be started, the arm 0 of rheostat R is gradually 
moved, cutting out resistance. 

The speed of a motor can be made to vary, first, by 
adding resistance in the armature circuit. This we 
have seen will tend to slow it down. Second, by in¬ 
creasing the strength of the field it can also be made 
to run slower. With a stronger field not so much 
armature sneed is necessary to develop a given counter 














78 


Operating and Testing 


E.M.F. and as this can never exceed the E.M.F. of the 
dynamo it follows that the motor must slow up. Con¬ 
versely, by weakening the fields we can increase the 
speed of the motor, but if the fields are weakened too 
much, the armature may not be able to do the work 
and the counter E.M.F. fall so much below that of 
the dynamo that the armature will burn out. 

The effect of a wrong position of the brushes is 
evidently quite different with motors than with dyna¬ 
mos. Suppose the brushes, Figure 55, to be moved % 
turn in the direction of motion. This will throw the 
N and S poles of the armature in perfect line with 
the polarity of the fields, and in this case the armature 
would have to come to rest. There would be no coun¬ 
ter E.M.F. and the rush of current w T ould burn up the 
armature wires. Again, suppose the brushes to be 
moved one-half revolution forward or backward, the 
direction of motion will be reversed. 

The magnetism of the N. pole of armature, of 
course, repels the magentism of the N. pole of the field 
just as it does in a dynamo. Hence with an increase 
of current through the armature which always fol¬ 
lows increase of load, the neutral line is shifted in the 
opposite direction in which the armature revolves and, 
to avoid sparking, the brushes must be shifted just 
in the opposite way to those of the dynamo. The 
same considerations that apply to short circuiting coils 
in an active part of the field of a dynamo apply to 
motors. The position of least sparking at the brushes 
is not, however, the position of greatest torque. 
The greatest pull is obtained when the brushes are set 
somewhat back of the neutral. If the brushes are 


Principles of Electric Motors—Direct Current 79 

shifted in either direction far from the neutral line, 
some of the coils will not be generating any counter 
E.M.F just as in the dynamo, and, consequently, if the 
motor is running empty, it will speed up. If the mo¬ 
tor is loaded, the armature will not be able to pull the 
load and slow down and very likely burn up. 

The maximum speed of any motor is that at which 
its counter E.M.F. most nearly equals the E.M.F. of 
the circuit. This speed can be approximately at¬ 
tained when the motor is doing no work. 

The losses in the motor are due to the same causes 

as those in the dvnamo. A certain amount is due to 

«/ 

friction. There is a loss of potential due to the re¬ 
sistance of the line and a further loss due to the arma¬ 
ture resistance. This in the armature, if excessive,, 
will manifest itself by much heating. 

If the fields are wound with a few turns of large 
wire instead of many turns of fine wire an unneces¬ 
sarily large current will be required for magnetiza¬ 
tion. If a poor quality of iron is used in the fields, 
or if the air gap between pole-pieces and armature is 
too great, the magnetic circuit will be of low conduc¬ 
tivity (see chapter on magnetism) and require un¬ 
necessary power to generate. 


CHAPTER VII 


TYPES OF MOTORS—DIRECT CURRENT 

There are as many different types of motors as 
there are of dynamos. Any dynamo may be used as a 
motor and any motor as a dynamo, as we have seen 
in another chapter. It is merely a question of apply¬ 
ing current properly. 

In the matter of regulation, however, there is con¬ 
siderable difference. We shall begin our study with 
the oldest and now almost obsolete form—the con¬ 
stant current series motor. This motor is made only 
in small units and used only on arc light circuits. 
The amperage of an arc light circuit does not usually" 
exceed ten amperes. To obtain even 5 H. P. with 
ten amperes would require a voltage of about 400 
volts, hence it can readily be seen that such motors 
are not commercially practicable except in small 
units and then only when no constant potential cir¬ 
cuit is available. 

The torque or pull of any r series motor, if the fields 
are not oversaturated, is proportional to the square 
of the current. Doubling the current doubles the 
strength of fields, and as the same current passes 
through the armature its strength is also doubled, 
hence the power of the couple is quadrupled. 


80 


Types of Electric Motors—Direct Current 81 


We have seen in a previous chapter that the speed 
limit of any motor armature is that speed at which 
the counter E.M.F. is equal to the E.M.F. existing at 
its terminals. These two can of course only be equal 
when no current is flowing, i. e., when the motor is 
doing no work. As we are here dealing with a cur¬ 
rent which is kept at a certain value by the dynamo, 
we need take no precautions to keep the current from 
damaging the motor. If now such a motor be started 
with a load it will at once develop its full torque or 
pulling power, the maximum current being instantly 
available in fields and armature. The torque will also 
be constant since field and armature are of constant 
resistance. The counter E.M.F. of the motor lias no 
effect upon the circuit except to require the genera¬ 
tor to work at a higher pressure. The speed of such 
a motor will vary as the load put upon it. If the load 
be removed from such a motor it will increase its speed 
and oppose the dynamo E.M.F.; this in turn will be 
increased and again the motor speed will be increased 
in a vain endeavor to build up an E.M.F. equal to 
that of the dynamo. If this racing of the motor is 
not checked by an increase of load or a regulator of 
some kind it will continue to speed up until it flies 
to pieces. The speed regulation of this motor is 
usually accomplished by reducing the field strength 
as the load decreases and increasing it as the load in¬ 
creases. The methods employed are similar to those 
illustrated in Figures 40 and 41. 

We mav next consider a similar motor on a constant 
potential circuit. The torque in this case is propor¬ 
tional to the sauare of the current as above. But in 


82 


Operating and Testing 


•this case the generator is without control over the 
current. If current is turned on suddenly before the 
armature is in motion there is only the ohmic resist¬ 
ance of the line, fields and armature to prevent it from 
rising to an enormous value. In well designed instal¬ 
lations these are all low and the result would be a 
burned out armature. Hence the resistance R, Figure 
57, is provided. This motor loaded down will act as has 
been described under Principle of Motors, the anna- 




W#N#N 


Figure 57 


ture tending to run at a speed at which it develops a 
counter E.M.F. equal to the E.M.F. existing at its 
terminals. With a heavy load the motor must slow 
down considerably to permit the necessary current for 
doing the work to pass. As the load is removed the 
current flowing becomes less because the motor speeds 
up and the counter E.M.F. begins to rise. This in 
turn weakens the fields Weakening of the fields les¬ 
sens the counter E.M.F. of the motor and consequently 









Types of Electric Motors—Direct Current 83 


it speeds up to make up for this. As the motor speeds 
up more and more the fields become gradually weaker 
and weaker, thus calling for still more speed in an 
endeavor to bring the counter E.M.F. up to the initial 
E.M.F. of the dynamo. This speeding up of a series 
motor without load will continue until the armature 
Hies to pieces. For this reason such motors are as a 
rule used only where an attendant can be kept con¬ 
stantly with them. 

As a rule this motor is used only in street railway 
work and on cranes, etc. In this case an attendant is 
necessary anyway. The motor because of its great 
starting power is best suited for this work, and any 
other kind of motor would moreover be entirely un¬ 
suitable, because very often the current is suddenly 
stopped or put on because of the trolley wheel leaving 
the trolley. With this type of motor there can be 
no current through the armature unless there is the 
same current through the belds. Consequently every 
rush of current (the armature being in motion, as it 
always is when the wheel for an instant leaves the 
trolley) is met by the proper counter E.M.F., which 
prevents undue current dow, and there is no need 
of regulation unless the speed of the armature has 
been much reduced during the time current dow was 
interrupted. 

The motor most in use for general work is known 
as the shunt motor. The belds and armature of this 
motor are entirely independent of each other. In 
operating this motor it is necessary to see that full 
current is in the belds before any current is allowed 
to pass into the armature. The armature current 


84 


Operating and Testing 


must then be turned on gradually so as to give the 
armature time to get in motion and develop the neces¬ 
sary counter E.M.F. before the full current is turned 
on. This is accomplished by means of the rheostat 
R shown in Figure 56. The speed of this motor is 
nearly constant under variable load within proper 
limits if it has been well designed and installed with 
low resistance in armature and line. It cannot be 
used in connection with street car work, principally 
on account of the inductance of its fields. The fields 
of a shunt motor always contain a great many turns 
of wire, and it requires some time for the current to 
attain its full value in them. If the current were cut 
off from such a motor for, say, a second and then ap¬ 
plied again, as often happens in connection with trol¬ 
ley service, the fields would in that second have lost 
their magnetism and upon the connection being re¬ 
established the motor would be running without fields 
and, of course, without its proper counter E.M.F. 
This would invite a very strong flow of current 
through the armature before the fields have time to 
build up, and furthermore a good armature without 
counter E.M.F. would offer almost no resistance and 
be equivalent to a short circuit and this would entirely 
prevent the fields from getting current so that either 
a fuse or circuit breaker would go out or the armature 
would burn out. To prevent accidents of this kind 
rheostats with overload and underload switches have 
been devised which entirely disconnect the motor if 
the current fails. 

The compound motor varies from the shunt motor 
just as the compound dvanmo does from the shunt 


Types of Electric Motors—Direct Current 85 

dynamo. A compound wound motor may, however, 
be used in two ways. If the current in the series 
winding is in the same direction as that in the shunt 
winding the fields will be strengthened as the load is 
increased. This will enable the armature to develop 
its counter E.M.F. with a lesser number of revolu¬ 
tions and therefore it will slow up. The power of a 
compound motor so connected will increase as the 
load is increased but the speed will decrease. 

If the current in the series fields flows in the oppo¬ 
site direction to that in the shunt fields the magnet¬ 
ism in the fields will be lessened as the load increases. 
This will force the armature to move at a higher rate 
of speed in order to develop an E.M.F. equal to the 
E.M.F. at its terminals. If the series fields are prop¬ 
erly proportioned to the shunt fields and the resist¬ 
ance of armature and line, the motor will run at a 
uniform speed with any load within its capacity. It 
will be noted, however, that the current through the 
annature with such a motor increases as the load in¬ 
creases much more rapidly than with an ordinary mo¬ 
tor since it must make up for the deficiency created 
in the fields by the opposing magnetism. The capac¬ 
ity of two identical motors, one shunt wound and the 
other ‘ ‘ differential, ’ ’ as this winding is termed, is 
therefore not equal, the differential motor having a 
much smaller capacity. 

As the differential motor uses power to neutralize 
power, i. e., the current in the series fields acts against 
that in the shunt fields, its efficiency is lower than that 
of any other direct current motor and its use in gen¬ 
eral is not to be recommended except where great 
constancy of speed is absolutely necessary. 


CHAPTER VIII 


PRINCIPLES OF ALTERNATING CURRENT MOTORS 

Many of the types of small direct current motors 
may be run on alternating current circuits. That this 
is true is readily apparent when it is recalled that 
changing the direction of flow of current in a direct 
current motor (both fields and armature) does not 
reverse its direction of rotation. When current flows 
through the motor in a positive direction, for instance, 
there is a certain attraction between those poles set 
up by the field current and those poles set up by the 
armature winding. If the direction of flow of cur¬ 
rent is reversed each of these sets of poles is reversed 
and the same attraction exists as before. 

Every coil of wire wound on an iron core, as in the 
case of a field magnet, has a certain inductance, which, 
when an alternating current is sent through it, acts 
as a resistance and tends to cut down the current 
flow. It is due to this fact that the majority of di¬ 
rect current motors, especially the larger sizes, can¬ 
not be used on alternating current circuits. If a di¬ 
rect current motor were constructed without iron 
either in the fields or armature it would operate on 
alternating current as well as on direct current. This 
characteristic is taken advantage of in some forms of 


86 


Principles of Alternating Current Motors 87 

integrating watt-meters which are suitable for use on 
either direct or alternating current circuits. 

If two identical alternating current generators were 
run, one as a generator supplying current to the other 
as a motor, the one running as a motor would run in 
exact synchronism and at exactly the same speed as 
the one running as a generator, for every change in 
the force producing power in the generator would be 
reproduced in the motor. This can be more readily 
understood by a study of the effects in a simple case. 
Suppose two bi-polar machines each have an arma¬ 
ture consisting of a simple loop the ends of which are 



connected to two collector rings, as shown in Figure 
58. The fields of both the generator and the motor 
must be supplied direct current from some outside 
source. If the armature of the generator G is re¬ 
volved to the right, as indicated by the arrow, current 
would be induced in the moving coil in the direction 
show T n by the other arrow. This current flowing in 
the coil of the motor M wmuld set up poles, as indi¬ 
cated by the dotted line S N", and these poles w r ould 
be acted upon by the polarity of the fields, w^hich is 
permanent, as shown. A north pole N will attract a 
south pole S and repel another north pole. This re*. 




















88 


Operating and Testing 


suits in motion and the armature of the motor is re¬ 
volved toward the left. 

The successive steps for a half revolution are illus¬ 
trated by the figures in Figure 59, where the figure 
at the left represents the various positions of the gen¬ 
erator coil, 1, 2, 3, 4, 1', as it makes a half revolution. 
The several figures at the right show the resulting 
condition and corresponding position assumed by 
the motor armature. 1 represents the position of the 
armature, as shown in Figure 58. At this point the 
generator coil is generating its maximum current. 
This current flowing through the coil of the motor 




produces a field of force with a polarity, as shown in 
the head of the arrow, indicating an N pole, and as 
the generator armature is requiring at this point the 
greatest expenditure of energy to turn it so is the 
motor armature yielding its greatest turning effort. 

When the generator armature has revolved to point 
2 the conditions in the motor armature are as shown 
in 2. There is the same tendency to turn the motor 
armature as before, but as the current in the genera¬ 
tor armature is decreasing so is the tendency to turn 
in the motor armature likewise decreasing As point 3 
is passed the direction of the current produced by 








and also the po- 
Principles of Alters a t point 4 the con- 

are as shown at 4. It 
the generator armament in the motor arma- 
larity of the moto^opposite direction, with the 
ditions in the pb between the armature and 
will be notkb pea ted, and the motor armature 
ture is rioy eV c4 ve in synchronism with and at 
result £ e S p ee d as the generator armature, 
fieldcoil generator just described is in op- 
w jld connection made to the motor armature 
mis armature is at rest, it will be quite evident 
, the motor armature will not revolve, for, when it 
ssumes the position shown in 3, Figure 59, it will he 
on a dead center and there will be absolutely no turn¬ 
ing moment. 

In order that the motor armature may continue to 
revolve it must have acquired some momentum to 
carry it over the dead center and it must also move at 
such a speed that it will always he at or neai the dead 
centers when the dynamo current reverses. If it is 
not its movement will be opposed by the reaction be¬ 
tween the poles of its armature and fields and come 
to rest. For this reason it is necessary to bring single¬ 
phase synchronous motors up to synchronous speed 
by some outside means before connecting it to the sup¬ 
ply current. 

Some polyphase synchronous motors are so designed 
that they will bring themselves up to speed if started 
under no load. 

Owing to the fact that synchronous motors are not 
self starting and that some outside means must be 





employed to bring them 
due to the further necessity 
excitation they are seldom use 

mercial work, their use being coll s s P ee( ^ ar j^ j 

in such places where they can be usbF en e 

.... ‘ rv corn- 

con ditions. J 

If the field excitation of a synchrono 11111 ^ 8 
varied the power factor is also altered and°7 e 
ble by varying the exciting current to pro 
leading “current,” this causing the motor to 
the same effect on the line current as would be cauSv 
by the introduction of a condenser. This character¬ 
istic is sometimes taken advantage of to increase the 
power factor on lines where it is low. 

For the ordinary purposes for which motors are 
used neither of the motors just described is suitable, 
To be commercially practical a motor must be self 
starting and must be capable of starting under a load. 
It must require current from one source only, i. e., 
must be self-exciting. The “induction” motor ful¬ 
fills these requirements, and is the form of motor in 
most common use on alternating current circuits. 

The principles underlying the operation of a poly¬ 
phase induction motor can be gathered from a study 
of Figure 60. In this figure the heavy black lined 
circles represent the wires of one phase, A, and the 
light those of the other, B, of a two-phase motor. 
These windings are placed in the slots of the stator as 
shown at the top of the figure and the small circle C 
represents one of the bars of a squirrel cage arma¬ 
ture, as shown in Figure 62. This circle also marks 
in the different sections of the drawing 1, 2, 3, etc. 





Principles of Alternating Current Motors 91 



Figure 60 


the position of a steadily advancing pole, in this case 
a north pole. 

The wires A and B are traversed by two independ- 




















































































































































































92 


Operating and Testing 


ent alternating currents which are, however, always 
in the phase relation illustrated in Figure 61 and in¬ 
dicated as to direction by a cross for positive and a 
dot for negative. In Figure 61 that portion of the 
currents represented by the sine curves above the 
base line may be taken as positive and those below it 
as negative. 

To begin let us assume that the current in A is at 
a maximum, as shown under 1 in Figure 61; at the 
same instant the current in B is zero; under these 
conditions B will not be producing any lines of force 



Figure 61 


and A will be producing a magnetic field, as shown in 
1 in Figure 60, the lines of force encircling the wire 
in which the current is positive (flowing away from 
the observer) in the direction in which the hands 
of a clock move. This produces a north pole at the 
wire C. A moment later the two currents assume the 
phase relation shown under 2, Figure 61, and the 
field becomes now as indicated at 2, Figure 60. The 
currents in both sets of wires now being in the same 
direction the lines of force expand and encircle both 
of them and the north pole is moved further to the 




















Principles of Alternating Current Motors 93 

right. In another short interval A sinks to zero and 
B arrives at its maximum, as shown under 3, Figure 
61. This in turn produces the field conditions, as 
shown at 3, Figure 60. As the two currents continue 
to rise and fall always maintaining the same phase 
relation (90 degrees apart), the field continues to 
change with them, as shown further in 4 and 5. 

It will be noticed that all of the poles set up by the 
different convolutions are moving steadily from left 
to right, and it can also be seen that if we should re¬ 
verse the two phases the poles would shift in the 
opposite direction. 

If, while this shifting of poles is going on, the 
wire C should remain stationary it would cut the lines 
of force rapidly moving by it just as it would in any 
dynamo in which the lines of force were stationary 
and the wire moving. In this way currents would be 
induced in it. These currents would be in such a 
direction that the lines of force created by them would 
oppose the lines of force creating them. This oppo¬ 
sition between the wire C and the field would result 
in motion if C were free to move. If C were to move 
at the same rate of speed as the revolving field it 
would cut no lines of force and no currents would be 
induced in it. It can in practice never move at this 
speed because it would then have no torque. 

It can be seen from the above that the difference in 
speed between the revolving field and the wire C, or 
of an armature carrying many wires like C, must 
depend unon the load, and the greater the load the 
greater must be the difference in speed between the 
two. In other words, in order to carry a heavy load 


94 


Operating and Testing 


such an armature must slack up in speed sufficient to 
allow of induction enough so that the reaction be¬ 
tween the two currents may be sufficient to move the 
load. This difference in speed is spoken of as the 
“slip.” If the load is too heavy the motor will sim¬ 
ply come to rest and burn out. 

It can also be seen that, if instead of a squirrel cage 
armature or rotor we provide one with a regular ar¬ 
mature winding the induced currents can be brought 
outside of the machine and be controlled by resist- 



Figure 62 


ance like those of any dynamo or motor armature 
This is often made use of in large motors. 

The rotor of an induction motor acts like the sec¬ 
ondary of a transformer and if it is at rest while cur¬ 
rents are traversing the stator, the effect is the same 
as though a transformer were short circuited. For 
this reason these motors require enormous starting 
current for a short time, sometimes five or six times 
the running current. 

In Figure 62 is shown the armature of an induction 
motor. The armature consists of a laminated iron 



Principles of Alternating Current Motors 95 

core with partially closed slots through the outer 
edge. Insulated copper bars inserted in these slots 
are bolted to rings on each end of the armature and 
are thus short circuited. This is called the “squirrel 
cage” type of armature owing to its similarity to the 
ordinary squirrel cage. The field is also formed of 
laminated iron cores with slots across its face into 
which the field windings are placed. 

In some designs of induction motors the element 
which has here been called the “field” is made the 
revolving element, the ‘ ‘ armature ’ ’ winding being 
placed on the stationary part of the machine. The 
conditions, so far as the operation is concerned, re¬ 
main the same whether the armature or field revolves 
but certain peculiarities in the design of the larger 
size motors, especially, make it preferable to have the 
field revolve. 

The two terms “armature” and “field” have a 
rather indefinite meaning when applied to alternate 
current motors. The field is generally considered as 
that element which receives current from the line 
while the armature is that part in which current is 
induced. The more common term applied to these 
parts is “rotor” for the revolving element and 
“stator” for the stationary element, although owing 
to their similarity with a transformer the field is 
sometimes called the primary element and the arma¬ 
ture the secondary element. 


CHAPTER IX 


TYPES OF MOTORS—ALTERNATING CURRENT 

• 

Single phase motors may be made self starting in a 
manner illustrated in Figure 63. This figure shows 
a diagram of the connections of a split phase motor. 
There are two sets of field windings and each has a 
different reactance, that is to say, one will permit a 
more rapid rise of current strength than the other. 



This action is as follows. The two semicircles in the 
center of Figure 63 surround the armature shaft. 
There is also a circular piece which revolves with the 
armature and whidi normally while at rest closes the 
circuit through the fine wire winding at the center. 
When current is turned on there is a flow through tlio 


96 












Types of Motors—Alternating Current 


97 


heavy winding and also through the fine, but there 
is considerable difference in phase between these cur¬ 
rents and they set up a field, as already explained, for 
two phase motors. This causes the motor to start as 
a two phase motor and when it has attained its proper 
speed the circuit through the semicircle is opened by 
centrifugal force which causes the outer ring to spread 
out. The motor now runs as a single phase induction 
motor. 


r> 


Figure 64 

Another form of motor is shown in Figure 64. The 
armature contains a direct as well as alternating cur¬ 
rent winding. The motor is started by throwing the 
switch S (blades not shown) to the left. This sends an 
alternating current through the fields and armature 
and starts the motor. After it has come to speed the 
switch is thrown to the right; this sends the current 
through the alternating current side of the armatuie 
and also closes the direct current side through shunt 
fields and rheostat (the switch closes the connections 

































































98 


Operating and Testing 


at 1 and 2). The motor now is synchronous with 
separately excited fields, the field excitation being fur¬ 
nished by the D. C. side of the armature. 

The three phase motors up to a capacity of 5 H. P. 
are not usually equipped with starting devices. Such 
motors are self starting but require enormous cur¬ 
rents when starting with load. Sometimes these cur¬ 
rents are 5 or 6 times the running current. In order 
to allow such currents to be used at starting and still 
have adequate fuse protec,tion when running the 
method shown in Figure 65 is generally employed. The 



switch is thrown up to start and the current does not 
pass through the fuses. After the motor is running at 
its normal speed the switch is thrown downward, 
thus forcing the current to pass through the fuses 
and protecting the motor As an extra safeguard the 
switch in ito first position is sometimes forced against a 
spring which would throw it out of connection if left 
there, thus assuring that the attendant will remain 
with it until the motor is running so he can throw 
it to the Mining position. 


















Types of Motors—Alternating Current 


99 


Polyphase motors are essentially constant speed 
motors. Any regulation of their speed is quite un¬ 
economical. They are all self starting and all subject 
to the same heavy rush of current at starting, as noted 



a N the smaller sizes only the stator carries 
dess for some special reason the rotor is 
The general appearance of the stator 



winding is shown in Fiabre gg 
winding and the win Jilts 
around. Diagrammat \ v ' * 1S a 
represented as in F^ure V 1Tl di]l the way 

/ re usually 








100 


Operating and Testing 


The windings of the three phases are shown in 
Figure 67. If we connect adjacent ends together we 
shall have what is known as the delta or mesh winding. 
If instead we connect the ends 1, 2, 3 together, we ob¬ 



tain the Y or star winding If a motor connected up in 
Y be changed to delta it will require much more cur¬ 
rent. If connected from delta to Y it will require less 
current. Of course, in both cases the heating w 



*H>t be recklessly made. 

n age with char' -u of girting induction mo- 

Change in con^ e 1 1*- ->, ists in inserting 
There are^se- 

tors in g enf 
























Types of Motors—Alternating Current 101 


resistances in the rotor circuit, as illustrated in Figure 
68, at R. This is commonly used only with the larger 
motors. This resistance may be so proportioned that 
the starting power of the motor will be just as great 
with it in circuit as without it, and where great start¬ 
ing power is necessary this is a very useful method. 

For the smaller and cheaper motors above 5 hr. P., 
the method shown in Figure 69 is mostly used. While 
the switch is in the position shown the current must 
pass through the auto transformer R. The amount of 
reactance can be adjusted by connecting the wires, 1, 
2, 3, at different points on R. The more reactance 
there is placed in the circuit the slower will be the 
starting of the motor. When the motor has attained 
sufficient speed the switch is thrown up and the cur¬ 
rent at full voltage goes direct into the motor. 


CHAPTER X 


DYNAMO OPERATION—DIRECT CURRENT 

The dynamo room should be so situated that it is 
not exposed to moisture or the flyings of dirt and 
combustible material. There is nothing that will help 
induce an engineer to keep appliances in good work¬ 
ing order more than a well ventilated and lighted 
room. 

The larger dynamos are now generally direct con¬ 
nected, and should be placed upon foundations en¬ 
tirely separate from those of the building. This pre¬ 
caution is due principally to the vibrations caused by 
the engine. Where dynamos are belt driven there is 
very little vibration, unless the machine is entirely too 
heavy for the flooring upon which it is placed. 

Whatever the power may be, whether steam, water, 
gas or gasolene, it is of the utmost importance to see 
that the prime mover operates as steadily as possible. 
The slightest fluctuation in speed will show in con¬ 
nection with incandescent lights. For this reason it is 
preferable to have the engines used for the lighting 
entirely separate from all other work that may be 
going on. This, of course, does not apply to factories, 
where only an indifferent light is required, as much a» 
for central stations, where power is being sold. 


102 


Dynamo Operation—Direct Current 


103 


If belt driving is necessary the machinery should 
be arranged that the belting may run as near hori¬ 
zontal as possible and the direction of rotation should 



be such that the belt will pull on the under side. This 
allows the slack of the belt to hang downward on the 



upper side and increases the arc of contact, as illus¬ 
trated in Figure 70, whereas a belt operating as that 



shown in Figure 71, by its slack decreases its jT 
contact with the pulleys. Whenever it is necessary to 
arrange belting as in Figure 72, it becomes necessary 





104 


Operating and Testing 


to keep the belts very tight. This is apt to result in 
hot bearings and also increases the amount of power 
necessary to operate. 

It is best to choose belting that is considerably heav¬ 
ier than would be absolutely necessary to do the work. 
In order to obtain a certain amount of work from a 
belt there must be a certain pressure exerted by the 
belt upon the pulleys. This can be obtained by 
stretching a small belt very tight, but is far better 
obtained with a much larger belt operating with con¬ 



siderable slack. Such a belt will last much longer 
and will need very little attention, while the smaller 
will need continually to be tightened. The smoothest 
side of the belt should be run next to the pulley, as it 
makes the most perfect contact. The face of the pul¬ 
ley should be smooth, as all roughness tends to wear 
the belt and does not add a bit to the adhesion. Wher¬ 
ever practicable it is best to have belts made up end¬ 
less; especially where the speed is quite high. With 
slow speed belting the lacing will not cause much an¬ 
noyance, if it is well done. 












Dynamo Operation—Direct Current 105 

A good method of lacing is shown in Figure 73. 
The holes should he made rather oblong, as shown, as 
in this way we avoid cutting away so much leather. 
On no account should any laces be run crosswise of 
the belt on the side next to the pulley. 

In placing belts it is always best to put the belt 
upon the smaller pulley first. Never allow oil to 
come in contact with rubber belting. Use only tallow 
or castor oil on leather belting. Grease can be re¬ 
moved from leather belts by the use of turpentine. 

The generator or motor should always be provided 
with a sliding frame, so that it can be adjusted to suit 
the belt from time to time. If the belt is properly ar¬ 
ranged, there will be some lateral play possible at the 
generator shaft; this is essential to smooth running 
and helps to secure even distribution of the lubrica¬ 
tion. 

The tension on all belts that are run tight should 
be relieved when the belt is not in use. 

Double belts should not be used on pulleys of less 
than three feet diameter. 

The proportion between two pulleys close together 
should not be greater than 6 to 1. 

If one is limited to a certain width of belt the power 
can be increased by increasing the diameter of both 
pulleys in the same ratio. This will not affect the 
speed of the machinery, but will increase the speed of 
the belt and hence its power in the same ratio that 
the speed is increased. 

The width of a single belt can be found from the 
following formula: 

W = 1200 X H.P. -y V 


X06 Operating and Testing 

where W is the width of the belt in inches and V the 
velocity of belt in feet per minute. For double belts, 
use 800 instead of 1200. This formula will give belts 
of ample size and, if necessary, much smaller belts 
can be forced to do the work. 

STARTING-ARC DYNAMO 

Before attempting to start the dynamo the circuit 
should be tested out to see that it is complete. If this 
is found in order, the belts should be examined for 
tightness; the bearings should be well oiled; all iron 
tools, etc., should be removed from proximity to tlm 
machine lest they be attracted by the magnetism that 
will be developed and cause injury It will also be 
well for the operator to leave his watch, unless it is 
shielded against magnetism, as far as convenient from 
the dynamo. Many watches are brought to complete 
standstill by being brought too close to the fields of a 
powerful dynamo. 

These things all being in order, the dynamo may 
now be set in motion, and it should now be so shifted 
on the sides that the armature has considerable lat¬ 
eral play. This indicates that the belt is in proper 
position and also helps to distribute the oil and keep 
the bearings cool. 

If the machine operates at very high voltage, an in¬ 
sulated wooden platform should surround it on all 
sides, and this platform should be so placed and of 
such dimensions that no one can touch the machine 
without standing upon this platform This platform 
will be of no use unless it is kept perfectly dry, and 
to assist to this end should be well filled wit 1 ! shellac. 


Dynamo Operation—Direct Current 


107 


It will also be well for the operator, especially if he 
be a novice, to provide hinisef with rubber gloves, and 
these also to be effective must be kept dry inside and 
out. As a further precaution, the operator should 
make it a rule while working on pressures above 220 
volts, to touch bare metal parts with one hand at a 
time only. If this precaution is observed and if the 
body is kept well insulated from the ground there will 
be but little or no trouble experienced from shocks. 

If the frame of the machine is grounded it will help 
to make things safer for the attendant, but will place 
a greater strain on the insulation. It will then be 
impossible for any one to obtain a shock by coming in 
contact with the frame, but greater care must then be 
exercised to avoid touching bare live parts and the 
frame at the same time. 

Under no circumstances must one ever touch high 
potential wires while standing upon wet ground, 
boards, cement, metal connected to earth or upon any¬ 
thing that is not known to be a good insulator. 

The regulator should now be examined to see that 
it is in proper working order and runs smoothly. Next 
place the brushes in position so that they bear prop¬ 
erly upon the commutator. Before doing so, note that 
the armature is running in the direction called for by 
the position of the brushes. If it is not, one or the 
other must be changed about. 

The plugs may now be inserted into the proper holes 
on the board. If there is sufficient residual magnet¬ 
ism in the fields the machine will begin to generate 
and, by noting the ammeter, the rise in current can be 
observed. If the residual magnetism is weak or en- 


108 


Operating and Testing 


tirely absent, as sometimes occurs in new machines, 
or such as have been idle for a long time, it may not 
build up with all of the lights in the circuit. In such a 
case it is best to start the machine with one or two 
lights in circuit and when the current has attained to 
its full value to open, the circuit and force current 
through the other lamps. 

If there is no residual magnetism whatever, even 
this expedient will not suffice to start generation and 
current from some outside source, either from another 
generator or from a battery, must be caused to flow 
around the fields. Only a very small amount of cur¬ 
rent is required for this purpose. 

It is most important, however, that the current from 
such a battery flow around the fields in the same di¬ 
rection as the current from the armaure would flow. 
If this is wrong in the first trial, it is but necessary to 
reverse the battery connections. Sometimes a machine 
can be started generating by striking the metal of the 
fields with a hammer in a gentle way. 

When the machine is fully staited, the next point 
of importance is to see that the polarity is correct. 
Unless the current enters the arc lamps at the proper 
terminal, the lower carbon will be consumed at the 
fastest rate and will, in a short time, burn down to 
the carbon holders, which will in turn be speedily de¬ 
stroyed. If the polarity of the machine is wrong, it 
can be corrected by changing plugs, as explained un¬ 
der switching, or the polarity of the fields be reversed, 
or the leads to the armature changed, as indicated, 
in chapter on current generation. 

Other methods of determining the polarity are given 


Dynamo Operation—Direct Current 


109 


elsewhere, but the only one generally used in a case 
like this is that of observing the are lamps. The pos¬ 
itive carbon will heat to a greater extent than the 
negative and consequently will remain warm longer 
and also, if the lamp is burning right, the brightest 
light will be thrown downward, while if the other 
way a bright light and strong shadows will be thrown 
against the ceiling. 

If there are more lights on a circuit than one ma¬ 
chine can handle, two may be connected in series as 
shown in Figure 74. In such a case the regulator of 



one machine is generally cut out and the brushes set 
for the highest potential at which this machine will 
operate well. The regulator on the extra machine is 
then depended upon to take care of the variations in 
the number of lamps cut into the circuit. 

An expedient sometimes resorted to when a number 
of circuits are run from one machine as illustrated in 
Figure 75 and when there is an open circuit in one of 
them, is to cut out the bad line for a time by the plugs 
indicated by dotted lines at P, until the lights in the 
other circuit are burning full, then suddenly with- 


























110 


Operating and Testing 


draw the plug This throws the whole accumulated 
force of the machine into the bad line, and if there is 
any possibility whatever the current will jump the 
bad place and often times operate the circuit success¬ 
fully thereafter. This practice is known as “jumping 
in,” and should never be resorted to when any other 
method is available, as it may ruin the d}mamo or 
cause fire or a breakdown of the insulation somewhere 
along the line. 



Figure 75 


To shut down the dynamo we close the switch shown 
at S, Figure 74. This shunts the current around the 
fields, and leaves them wtihout magnetism, thus caus¬ 
ing the current to sink to zero. On no account except 
that of extreme emergency must a series circuit oper¬ 
ating at high potential be broken suddenly. Such an 
interruption causes an enormous rise of potential for a. 
very brief interval, which very often breaks down the 
insulation of the machine. The arc which follows the 
plug when it is suddenly withdrawn, is also often dan- 








Dynamo Operation—Direct Current 


111 


gerous to the operator. If, however, such a circuit 
must be opened it should be done with a rapid motion 
and the operator should station himself so that the end 
of the plug or wire cannot strike him. 


STARTING SHUNT DYNAMO 


In latter day practice it is very seldom that a shunt 
dynamo is used with variable potential or constant 



n n 

S Si 




Figure 76 


current systems. Such machines are limited to con¬ 
stant potential work and variable currents. The con¬ 
nections of a shunt dynamo and switchboard are 
shown in Figure 76. The same general considerations 
that apply to arc machines also apply here. 









































J lZ 


Operating and Testing 


To start the generation, we first disconnect the ma¬ 
chine entirely from the circuit. This is not always 
necessary, as many machines will build up success¬ 
fully with the whole load connected. Nevertheless, 
however, it is safer to disconnect the load. When 
the machine has been set in motion, we observe the 
voltmeter and by means of the rheostat R regulate 
the current through the fields, so that the voltage 
gradually approaches its proper value and remains 
stationary. When this point has been reached the 
main switch can be closed and the lights will burn. 

Unlike the series arc machine the shunt machine 
can do nothing while there is a short circuit on the 
line. There being no regulator the current immedi¬ 
ately rises to its highest possible value and the pres¬ 
sure of the dynamo sinks to zero approximately. This 
machine cannot be started while it is connected to a 
short circuit, because all of the current generated will 
flow through this “short,” which acts as a shunt to 
the fields. The “short” coming on while the machine 
is working wlil cause a momentary rise in current 
strength; it will also act as a shunt to the fields and 
deprive them of all current, thus finally reducing the 
E.M.F. of the machine until no more current is gener¬ 
ated If the armature is wound so as to stand this 
current for a fraction of a second, it will do no harm 
to the dynamo. 

In large installations it is customary to operate a 
number of dynamos in parallel. During the day, 
when the load is light, it will be taken care of by one 
of the dynamos and as the load increases more ma¬ 
chines will be connected to the board to help out the 


Dynamo Operation—Direct Current 


113 


first one. If we have nothing but plain shunt ma¬ 
chines, it is not advisable to attempt operation in par¬ 
allel. It is practically impossible to keep two shunt 
machines at the same potential, and the one having 
the higher voltage will take the greater part of the 
load and also, when the difference amounts to as much 
as a few volts, run the other as a motor. This acci¬ 
dent occurs frequently, and generally with so little 
disturbance that the attendants know nothing about 
it unless they happen to observe the belting or am¬ 
meters. 

When a number of plain shunt machines are to 
work on the same installation, it is best to divide the 
system and give each machine a share of it. If this 
cannot be done, the voltage of the two machines must 
be constantly watched and adjusted by means of the 
rheostat. 

For operation in parallel it is customary to provide 
compound dynamos. The arrangement of the wiring 
on such machines is such that when one machine takes 
more than its share of current it strengthens the fields 
of the other and thereby causes the potential of the 
other to rise until it draws its share of current. Com¬ 
pound machines when properly designed and driven 
by good engines, can be operated together with perfect 
freedom, no matter what the difference in capacity of 
the machines may be. 

The connection and operation of two or more com¬ 
pound machines can best be understood if we refer to 
Figure 77, which shows the machine and switchboard 
connections of two such machines. It is essential to 
see that the ammeters A are cut in, as shown in the 


114 


Operating and Testing 


diagram. If they are cut into the same side as the 
compound winding, the indications will be very unre¬ 
liable, since the current from this side of the machine 
has two paths through which it may flow to the board; 
one through the fields of the other machine and one 
through the main of its own dynamo. The equalizer 



Figure 77 


wire E should be of ample size, the lower the resisl 
ance of this wire the closer will be the regulation or 
the two machines. The main switches of the dynamoa 
should be so arranged that the equalizer will be con¬ 
nected slightly before the other two wires are and on 
no account later. In order that such dynamos may 
work at their best, they should be run at exactly the 































































































































Dynamo Operation—Direct Current 


115 


proper speed. If this is not the case, the relation be¬ 
tween the shunt and compound winding will be dis¬ 
turbed. If, for instance, the machine is run above its 
intended speed, the magnetization of the fields will 
have to be below the usual point of saturation, and in 
this case the magnetization due to the series current 
will be greater than it should be and the rise in volt¬ 
age higher than intended. If, on the other hand, the 
speed is much below normal, more resistance will have 
to be cut out of the field circuit, and thus the fields 
may be saturated by the shunt winding alone, so that 
the series current will have far less effect than it was 
intended to have, and the rise in voltage as the load 
increases will not be sufficient. 

Many machines are provided with resistances placed 
in parallel with the series fields, and by means of 
these the series fields can be strengthened or weakened 
and in a measure adjusted to make up for variations 
in speed if they are unavoidable. The location of 
such resistances is indicated at C. 

It will be well also to observe whether the series 
current circulates around the fields in the same direc¬ 
tion as that in the shunt winding. If it does not, the 
series winding will have the opposite effect of that 
intended, and there will be trouble and sparking at 
the brushes and a large falling off in pressure as the 
load is increased. 

To start a plant of compound dynamos we begin 
'Vith a single machine. When this has been brought 
ap to speed and is running smoothly, we close the cir¬ 
cuit through the fields by means of the rheostat R and 
adjust this resistance until the dynamo gives the re- 


116 


Operating and Testing 


quired voltage. It is better always to see that R is 
high at the start and gradually cut resistance out of it 
than to start with the resistance in R low. After the 
voltage is about up to its normal, we close the main 
switch. This, if there are many lights or motors us¬ 
ing current, will result in a modification of the pres¬ 
sure and we must again adjust R until finally it comes 
to a steady value at what it should be. 

If a load heavier than one machine can carry is 
likely to be found at the start, some of it had best be 
disconnected or circuit breaker or fuses may go out 
and cause delay. 

After the first machine is started the second is 

brought up to speed in the same way and the voltage 

% 

brought up as near as possible to that of the first ma¬ 
chine when the main switch may also be thrown in. 
When this is done, it will be necessary for the attend¬ 
ant to observe the ammeters of both machines care¬ 
fully and quickly adjust the rheostats so that each 
machine will receive its proper share of the current. 
It must be borne in mind that the machine with the 
higher voltage will take the greater part of the load, 
and if sufficient difference of potential develops be¬ 
tween them it will run the other as a motor. 

Before a newly set up machine is thrown in with 
another, it should be tested for polarity. In order 
that they may operate properly, similar poles of all 
machines must connect to the same bus bars. Two 
simple methods of testing for polarity are illustrated 
in Figure 78. At the left two lamps of the voltage of 
the machines are connected between the dynamos to 
be started and the bus bars, as shown. When the dy- 


Dynamo Operation—Direct Current 


117 


namo to be thrown in is np to voltage, the pressures of 
the bus bars and this dynamo must balance, and there 
can be no noticeable current flowing through the 
lamps. If, however, the polarity of the new dynamo 
is different from that of the others, the voltage of the 
system will be double that of one dynamo and the 
lamps will burn at full candle power. If the lamps 



Figure 78 


are dark, the polarities of the dynamos are correct for 
parallel operation. 

In lieu of the lamps the test can be made by insert¬ 
ing one wire from each pole of the dynamo into a cup 
of water and noting the bubbles that form. If the 
polarity is correct the bubbles will form at the same 
pole of the switch on both machines. To avoid making 














118 


Operating and Testing 


short circuits with this test, the bare ends of the two 
wires may be wrapped about a piece of wood about 
an inch long and the whole immersed in the water. 
Connect the same wires, one at a time, to the same 
poles of both switches and see that the bubbles come 
from the same wire. 

A switch board arrangement often used with either 
shunt or compound machines, when engines regulate 
poorly, or in machine shops and other places where 
trouble from grounds or short circuits on large motor 
units are frequent occurrencies, is shown in Figure 



79. In many machine shops, for instance, the capac* 
ity of the motors connected is four or five times as 
great as that of the generators. The assumption is 
that only a small part of the motors will ever be op¬ 
erating at the same ime. When, however, the motor 
load exceeds the capacity of the generator, as it some¬ 
times does, the generator fuses blow and place the 
whole installation in idleness. This is also likely to 
occur in case of trouble on a single large motor, such 
as are used for metal saws, etc. For the above reasons 
it is preferable to divide the plant into sections, as 











Dynamo Operation—Direct Current 


119 


shown. It will be noticed that any or all of the load 
may be thrown onto either set of machines by means 
of the throw over switches in the center row. Any 
desirable division of the load can thus be made. Office 
lights, for instance, can be separated from the large 
motors that are constantly disturbing the equilibrium 
of the lines. 

In transferring motors from one machine to the 
other it is necessary to allow time enough for the au¬ 
tomatic release to operate before the switch is closed 
on either set of bus bars, otherwise the motor is likely 
to be subject to a severe rush of current if its speed has 
fallen off much in the interval. If the motor is run¬ 
ning light and has great momentum, the switch can 
be thrown over quickly without much fear of dis¬ 
turbance. 

Shunt or compound dynamos if running singly, 
and if not supplying motors, may be shut down by 
simply shutting off the engine and letting them come 
to rest. If, however, there are motors connected to 
the dynamo, these must be disconnected before the 
voltage of the dynamo is allowed to go down. A mo¬ 
tor heavily loaded may stop entirely when the E.M.F. 
at its terminals drop off, say twenty-five per cent. It 
will then be without counter E.M.F., and the arma¬ 
ture will form a dead * ‘short’ * which will blow fuses. 
The automatic release on the rheostat must not be re¬ 
lied upon in a case like this. 

If there are several dynamos operating in parallel 
and one is to be shut down, it must be disconnected 
from the switchboard while nearly at full pressure. 
The pressure may be reduced only sufficient to trans- 


120 


Operating and Testing 


fer the greater part of the load upon the machine 
which is to remain in service. If it is reduced more 
than this, the dynamo will be run as a motor by the 
other machine. 


COMPENSATORS 

Compensators, equalizers, or balancing coils are 
used in connection with high voltage generators to 
allow of the operation of lights or other devices at 
half the voltage of the dynamo. They also come in 



convenient for the operation of variable speed motors 
since they make two voltages available. 

Figure 80 shows the connections of the system used 
by the Westinghouse Co. The armature of the dy¬ 
namo is connected so that it can produce both alter¬ 
nating and direct currents. The main current is di¬ 
rect and there is just A. C capacity enough provided 
to take care of the unbalanced portion of the load, 
which is usually estimated never to exceed 25 per cent 
of the capacity of the generators. 














































Dynamo Operation—Direct Current 


121 


All full voltage apparatus is connected to the + and 
— buses, and the half voltage equally distributed 
from the neutral and the two outside wires, so that 
the load will always be balanced as near as possible. 
The balancing coils B have the appearance of trans¬ 
formers, but carry no secondary winding. Their ob¬ 
ject is merely to provide a point at which only half of 
the voltage of the generator shall exist. Once properly 
connected they require no further attention except 



to see that the load is not unbalanced beyond their ca¬ 
pacity. 

As more or less of the load may come on either 
side of the dynamo the compound winding is divided 
between both sides of the generator, which makes it 
necessary to run two equalizer wires, as shown. An 
ammeter for each dynamo lead should also be pro¬ 
vided. Volt meter and shunt field connections are 
not shown in this figure, as they are the same as with 
ordinary generators. 








































122 


Operating and Testing 


The connections of a balancing set as arranged by 
the Western Electric Co. are shown in Figure 81. 
Here two differentially wound motors are connected 
to the same shaft, so that they must run at the same 
speed. So long as the same number of lights are burn¬ 
ing on both sides of the neutral wire the current 
through both motors is the same, and they perform no 
work, but keep in motion. 



The action of the set can best be comprehended from 
observation of the elementary diagram, Figure 82. 
With the load unbalanced as shown, current from the 
generator will pass through motor A and supply some 
of the excess load on the opposite side. As this cur¬ 
rent is in opposition to the shunt fields, it will weaken 
the motor fields and hence speed it up. This speeding 



































Dynamo Operation—Direct Current 


123 


up will also affect the other motor, the fields of which 
are not weakened, and hence cause it to act as a gen¬ 
erator, thus helping to supply some of the excess load. 
If the excess load appears upon the other side the 
conditions will be reversed. Either motor may act as 
a generator or motor, as conditions require. 

The field rheostat is used to equalize the voltage of 
the two machines and should be placed in the stronger 
field. Very often the coil on the starting box serves 
to unbalance the fields and must then be arranged on 
the opposite side from the field rheostat. 

In old installations the capacity of compensators is 
sometimes overtaxed by the addition of too many 
lights or motors. In such a case an artificial balancing 
load is often added, as shown at L. The lamps there 
shown may be connected to either side of the system, 
as the case may require. 

Storage batteries, as shown in Figure 128, can also 
be used for purposes of balancing as above. 


CHAPTER XI 


OPERATION OF ALTERNATORS 

The operation of a single phase alternator working 
alone is not much different from that of a direct cur¬ 
rent machine. Such machines may be compound 
wound, as illustrated in Figure 53, in which case that 
part of the current which circulates around the fields 
must be made to circulate always in the same direc¬ 
tion, as in direct current machines. This is accom¬ 
plished by means of the rectifier shown in Figure 53. 
Each of the sections of the rectifier are in connection 
with one of the collector rings and subject to changes 
in the direction of current in the same way as the 
collector rings. The rectifier is mounted upon the 
same shaft as the armature and moves with it in such 
a manner that whenever the current in the armature 
falls to zero the change of brushes from one section 
to the other occurs. 

So long as the brushes are set in this position there 
is no sparking, but since there is considerable varia¬ 
tion in the inductance of an alternating circuit the 
current is not always at 0 when it should be and, 
therefore, at times there is very severe sparking. 
Compound wound alternators are, therefore, not much 
used at present. 


124 


Operation of Alternators 


125 


Some generators have two brushes in each lead of 
the rectifier. The trailing brush is set permanently 
and the leading brushes alone are changed with 
changes in the inductance of the load. All alternators 



Figure 83 


are separately excited by means of a direct current 
dynamo and the first step, therefore, is to bring this 
exciter in running order. This is done in the same 
manner as with shunt dynamos previously explained. 

Figure 83 shows two alternators connected to a 




























































































































126 


Operating and Testing 


switchboard. The instruments are operated through 
suitable transformers, as is customary with high ten¬ 
sion installations. Both machines are excited by the 
same dynamo, but each, of course, has its own field 
rheostat, and there is a third rheostat for the exciter. 
The operation of alternators in parallel, though prac¬ 
tical, is somewhat difficult, and requires close atten¬ 
tion on the part of attendants; it is therefore often 
avoided, and the switchboard shown is divided so that 
each machine can take care of part of the load without 
being connected to the other. By means of the over¬ 
throw switches any or all of the lights or motors may 
be connected to either of the machines. Transfer 
from one machine to the other may be made at any. 
time without shutting down motors, provided, of 
course, the machine will not be overloaded thereby. 
If a very large motor, however, happens to be heavily 
loaded, it is best to shut it down and start it again 
after transferring. 

In order to operate alternators in parallel, several 
precautions are necessary: 

They must all run very closely at the same speed 
and the fluctuations in speed must vary in about the 
same degree and occur at the same time. 

The E.M.F.S of the machines must be the same and 
they must be synchronized, i. e., they must pass 
through their respective maximum and minimum val¬ 
ues at the same time. In order to get a clearer under¬ 
standing of this refer to Figure 84. This figure shows 
two series of sine curves, which represent the currents 
of two machines. Both machines are working at the 
same E.M.F., but*the one represented by the lower part 


Operation of Alternators 


127 * 


of the figure moves through eight cycles in the same 
length of time that the upper passes through seven. 
Beginning at the left the polarities of the dynamos are 
exactly opposite at the same time and there can, there¬ 
fore, be no cross currents between them. Gradually 
the lower machine gains on the other until at the cen¬ 
ter of the figure one is positive and the other nega¬ 
tive; at this point they are working in series instead 
of parallel, which is equivalent to a dead short cir¬ 
cuit, so that all of the current circulates between the 
two machines and none of it goes out to the line. Con¬ 



tinuing still farther at the right, they are again op¬ 
posed to each other and working in parallel. It will 
be seen at once that tw r o dynamos working in this 
manner cannot be coupled together without causing 
serious damage to both of them. 

In order to attain smooth and economical operation 
it is necessary that both machines keep together in 
speed at all times. If they are nearly so a slight cur¬ 
rent from the leading machine passing into the lag¬ 
ging one will help operate it and thus speed it up to 
keep pace with the other, but the less of such a cur¬ 
rent is necessary the better it is. 






128 


Operating and Testing 


If such dynamos are operated from a common shaft 
it will be well to leave the belt of one of them slack 
so that the other can easily force it into synchronism. 
If they are operated by separate steam engines, the 
piston strokes of the engines should be synchronized. 
Referring to Figure 85, it can be seen that the engine 
receives nearly if not all of its power during the time 
that the crank pin is moving from 1 to 2 and from 3 to 
4. During the time it is moving from 2 to 3 and 4 to 1 
the steam is not only shut off, but some of it actually 
forms a cushion, which checks the motion. While 
these differences in speed caused in this way are not 



perceptible to the eye, they are sufficiently great to 
cause very damaging cross currents to circulate be¬ 
tween the dynamos. 

There are some specially designed machines that 
do not require such close synchronization. Such ma¬ 
chines are provided for operation in connection with 
gas engines. These engines often miss fire and drop 
the whole load for an instant, and it is no unusual 
thing to see the ammeters of such machines swinging 
from zero to the maximum. 

In operating two alternators in parallel we begin 
by starting the first one, bringing it up to its proper 
voltage and speed and giving it about the load it 


Operation of Alternators 


129 


should caisry. The other machine is next started and 
if it has not been tried before the first step is to test 
it for polarity, i. e., to see that similar poles of both 
machines connect to the same bus bars. The simplest 
method of doing this is shown in Figure 86, but this 
method must not be used with high tension work. If 
the polarity of the second machine is right, the lamps 
shown at L will all be bright and dark at the same 
time. If the machines should accidentally be in phase 
with each other, the lamps would be dark continually, 



Figure 86 


but as this will probably never occur they will alter¬ 
nate between light and dark with more or less rapid¬ 
ity. If the lamps do not go up and down together, 
two of the leading wires from one of the machines 
must be changed until the lamps are operating to¬ 
gether. Lamps used for this purpose must be capa¬ 
ble of standing double the pressure of the system Since 
the only time at which they will be bright is when 
the dynamos are coupled in series and at double volt, 
age. 



















130 


Operating and Testing 


The polarity of the machines being in order, the 
next step is to bring them in synchronism. There are 
different methods of doing this, illustrated further on, 
so we shall give here one of the simplest methods, but 
one that is suitable for low voltages only. In Figure 
87 one synchronizing lamp is provided for each dy¬ 



namo, as shown. Suppose dynamo A to be running 
and that B is to be put in parallel with it. By closing 
the switches 1, 3 and 4, circuit is established through 
the two lamps and similar phase wires on the two ma- 
.chines and the lamps are connected to two similar 
wires. If the voltage of the two wires is the same and 
the maxima occur at the same time the lamps will be 

































































Operation of Alternators 


131 


dark and remain dark as long as the above condition 
prevails. But if one machine moves faster than the 
other, the same effect described before will be noticed 
on the lamps, viz: they will alternately light up and 
become dark. The nearer synchronism the two ma¬ 
chines are the longer will be the periods of light and 
darkness. The new machine must now be regulated so 
as to bring it nearly to the same speed as the other, 
and at about the middle of one of the dark periods 
when they are of several seconds duration the switch 
may be thrown in and the dynamos allowed to work 
together. 

It is not possible to divide the load between alterna¬ 
tors by simply raising the voltage of one machine, as 
is done with direct current machines. In order to 
increase the current in one of the machines, the engine 
driving it must be made to do more work by giving it 
more steam, and a governor by which this can be done 
must be provided. Giving an engine more steam will 
cause it to speed up a little and thus create a slight 
cross current, which will help drive the other. If a 
very great load is to be shifted from one dynamo to 
another, it is best to speed up the dynamo as above 
and also to increase its voltage a little, and to perform 
both operations by small steps, a little increase in 
power, then a little increase in pressure, a little more 
power and a little more pressure, etc. 

The currents circulating between two machines dif¬ 
fering only in voltage are wattless and do nothing but 
heat the wires. In order to get the best distribution 
of load an indicating watt meter should be placed in 
the circuit of each machine and the watts of both of 


132 


Operating and Testing 


them kept in proportion to the capacity of the ma¬ 
chines. If such instruments are not at hand there must 
be an ammeter for each, and there should be a main 
line ammeter which measure the total current. If the 
sum of the machine currents is greater than the total 
line current, it is an indication of cross currents flow¬ 
ing between the machines. The dynamos must be sc 
adjusted that the sum of the dynamo currents becomes 
a minimum. When this is the case the cross currents 
are at their lowest value. 

The rheostats of the different machines should be 
worked in such a manner that the voltage of the line 
is not affected more than absolutely necessary while 
distributing the load. This is done by working the sev- 
ral rheostats a little at a time; increasing one and de¬ 
creasing another, thus trying out how best the load 
can be distributed without changing the voltage of the 
system. If there is a power factor meter for each 
machine, they should be made to read alike and this 
will indicate that the machines are working properly. 

Some of the larger systems using alternating cur¬ 
rents have two systems of bus bars that may be used 
in parallel or may be separated when occasion re¬ 
quires. When such are to be connected in parallel 
there are two groups of generators to be synchronized 
instead of single machines. This is generally accom¬ 
plished by taking one or more generators out of service 
of the group which is running at the higher speed. 
This forces the total load on one engine less and thereby 
causes the whole group to run slower. When thus the 
two groups are in synchronism they may be coupled 
together. 


Operation of Alternators 


138 


Rotary converters are operated in the same manner 
as alternators. They must be first brought up to speed 
by means of some outside source of power, usually an 
induction motor, or from the direct current side, and 
then synchronized. If there are several such convert- 
el's, the load must be divided between them bv 
strengthening the field of the one that is to take more 
current. 

By proper manipulation of the excitation the power 
factor of a given load can also be materially affected 
and occasional attempts to improve it will do no harm. 

The power factor of a line indicates the ratio of the 
true power transmitted to the apparent power. To 
find the real power being delivered by an alternating 
current system, we must multiply the product of the 
volts and amperes by the power factor. The power 
factor of a system supplying incandescent lights only 
is ordinarily about .95 while with induction motors it 
is often as low as .70, especially if the motors are not 
used at proper load. Whenever the power factor is 
low, the system is operating at poor efficiency. 

Long distance transmission lines are frequently de¬ 
signed for very great losses at full load. In such a 
case the voltage will be too low for satisfactory opera¬ 
tion when the full load is being used and if, to over¬ 
come this, the pressure of the dynamo is raised it will 
be too high on circuits that are not heavily loaded. 
In order to obtain satisfactory operation under such 
circumstances some means must be provided whereby 
the pressure on different branch circuits can be reg¬ 
ulated without changing the voltage of the dynamo. 

The Stillwell regulator is the best known of these. 


134 


Operating and Testing 


and is typical of all the others. Each regulator must 
be provided with two windings and is really a trans¬ 
former, the primary circuit of which is connected 
across the mains and the secondary in series with the 
main current. In Figure 88 S is a double throw 
switch, by means of which the primary coils Y can be 
connected so as to raise or lower the voltage of the line. 
By means of the handle C as much of the secondary 
winding can be inserted into the main circuit as may 
be found necessary, and this may assist or oppose the 
main line voltage. The inductance L is provided to 



Figure 88 


prevent serious short circuiting of any of the secondary 
coils while the contacts of C are moved from one seg¬ 
ment to another. It will be seen that C is split and 
that therefore during the time that it bridges two seg¬ 
ments the currents induced in the coil between them 
must pass through L. 

SYNCHRONIZERS 

To connect a direct current generator in parallel 
with a generator already running the voltage of the 


























Operation of Alternators, 


135 


generator to be connected must be adjusted to corre¬ 
spond with the voltage of the generator which is run¬ 
ning, or with the bus bars to which the generator is 
connected. When their voltages are alike the generator 
circuit may be closed. 

When alternating current generators are connected 
in parallel, the geneartor to be connected must not 
only correspond in voltage, but it must also be in “syn¬ 
chronism” with the other generators feeding into the 
bus bars. Two alternating currents are in synchro¬ 
nism when their phases coincide, or when all changes 
in their E.M.F.’s exactly correspond. Both must reach 
a positive maximum value at exactly the same time. If 
two generators were connected together when their 
E.M.F.’s were 180° out of phase, or when the E.M.F. 
of one machine was at a positive and the other at a 
negative maximum for instance, a direct short circuit 
would occur. The conditions would then be very simi¬ 
lar to those existing where a direct current generator 
with its polarity reversed was thrown in parallel with 
another machine. The positive of one machine would 
then be connected directly to the negative of the re¬ 
maining machine and a severe short circuit would re¬ 
sult. 

Where the currents of two alternators are only 
slightly out of phase, the incoming machine will be 
brought into step with those already running, but a 
considerable strain will be imposed on all the machines 
and considerable current will flow between them. In 
order to ascertain when two alternators are in synchro¬ 
nism, synchronizers are used. The simplest form of 
synchronizer consists of two incandescent lamps con- 


136 


Operating and Testing 


nected in series between the machines as shown by 
broken lines in Figure 89. 

If the brushes bearing on the same collector rings 
are to be connected together, or to the same bus bar, it 
is evident that when the two machines are in phase, or 
synchronism, the two brushes will at any moment be at 
the same potential and of the same polarity. The 
E.M.F.’s of the two generators being directly opposed 
the lamps connected between them will not burn. This 



Figure 89 


is called synchronizing “dark,” due to the fact that 
the lamps remain dark when the generators are in step. 
Suppose the currents in the two generators were 180° 
out of phase. When one of the collecting rings of ma¬ 
chine L is positive, the corresponding ring of machine 
M is negative and the two machines are then generat¬ 
ing in series. The two lamps will, therefore, bum at 
full candle power, the combined E.M.F.’s of the two 
generators being now impressed on the lamps. Two 
lamps of the same voltage as the generators or one 





























Operation of Alternators 


137 


lamp of a voltage suitable for the combined voltage of 
the two generators may be used. 

If the two generators continued to run under the 
same conditions as those just described, and did not 
change in speed, the two lamps would continue to 
burn at full candle power; but if one of the machines 
runs at a slightly slower speed, the positive maximum 
values of the E.M.F. of this machine would occur 
just a little later than that of the other, finally falling 
back to a point where the two generators come again 
in synchronism, at which point the lamps would be 
dark. As long as the generators are varying in speed, 
the lamps will alternately light up and go out, this 
change occurring more rapidly as the difference in 
their speed increases and gradually dying out as they 
approach uniformity. As they approach synchron¬ 
ism the intervals between the time of light and dark 
will grow longer and when a point is reached where 
the lamps stay dark for a considerable time, the main 
switch may be thrown in and the machines run to¬ 
gether. 

In synchronizing alternators, it is safer to close the 
main switches just before the point of synchronism is 
reached than after, as some little time is required to 
throw in the main switches. 

In order that the lamps may be used with either 
machine and without leaving them continually in con¬ 
nection with either of the machines they may be ar¬ 
ranged as shown in the center of the figure. The over¬ 
throw switch must be thrown towards the incoming 
machine. 

The use of synchronizing lamps, as shown in Figure 


138 


Operating and Testing 


89, is limited to low voltages. Transformers may be 
connected in the generator circuit, as shown in Fig¬ 
ure 90. This arrangement allows the use of ordinary 
voltage lamps, irrespective of the voltage of the gen¬ 
erators. If the transformers are so connected that 
their secondaries oppose each other when the genera¬ 
tors are in step the darkness of the lamp will indicate 
the point of synchronism. If either one of the prima¬ 
ries or secondaries of the transformers are reversed 
the transformer secondaries will be in series and assist 
each other and the point of synchronism will be indi¬ 



cated by the lamp burning at full brightness. This is 
known as synchronizinz “bright.'’ Either method, 
may be used and both have their advantages and disad¬ 
vantages. 

If both of the plugs used make the same connection 
as indicated at 1 and 2, the lamps will be dark at 
synchronism; if one of the plugs reverses connections, 
as at 3, the lamps will be bright at synchronism. When 
the machines are running together the synchronizing 
bus is entirely disconnected. When synchronizing 
bright, the eye becomes more or less fatigued by con¬ 
stantly watching the lamp and the point of full bright- 












Operation of Alternators 


9 


139 


ness may be misjudged. On the other hand an incan¬ 
descent lamp requires considerable voltage before the 
filament becomes visible and darkness does not neces¬ 
sarily denote that no current is flowing, or the fila¬ 
ment may be broken during the time of synchroniz¬ 
ing. To" overcome these objections mechanical syn¬ 



chronizers have been devised and are now generally 
used, which will not only accurately indicate the ex¬ 
act point of synchrony but will also show which ma¬ 
chine is running too fast or too slow. 

The Lincoln synchroscope is a device designed for 
this purpose. The principle of its operation may be 








































14U 


Operating and Testing 


understood by reference to Figure 91, where F rep¬ 
resents a stationary field supplied with current 
through the two lower binding posts on the instrument 
to one of the generators. The two coils G and H at 
right angles to each other, are mounted on a shaft and 
are free to revolve about their common axis. The 
windings of the movable coils are brought to a com¬ 
mon junction and carried to a slip ring mounted on 
the shaft, connection being made from this point to a 
binding post at the top of the instrument. The re¬ 
maining ends of the coils are carried to two other slip 
rings. Connected in series with one of the coils is a 
non-inductive resistance (incandescent lamp) and in 
series with the other coil an inductive resistance or 
choke coil. From these resistances the connections are 
brought to a common point and carried to the remain¬ 
ing binding post. 

Connection is made from the binding posts 1 and 2 
to one of the machines to be synchronized and from, 
the other binding posts to the remaining machine. 
"When an alternating current is passed through the 
movable coils, there will be a phase difference of 90° 
between the current in coil G and that in coil H, and 
a rotating magnetic field will result. This rotating 
field acting in conjunction with the rapidly reversing 
field of coil F will cause the movable coil to revolve. 
A pointer attached to the shaft of this coil indicates 
the direction and extent of the movement. 

As long as the two generators vary in speed the 
pointer will continue to revolve, turning at a greater 
rate with a greater difference in speed and slower as 
the generators approach svnchronism. Should the 


Operation of Alternators 


141 


machine which was running faster, decrease in speed 
and run slower than the other machine, the pointer 
would revolve at a slower rate and finally run in the 
reverse direction. When the machines are running at 
exactly the same speed, the pointer will come to rest. 
If the machines are in phase the pointer will come to 
rest in an upright position; if out of phase, the posi¬ 
tion of the pointer will indicate the difference in phase 
between the currents in the two machines. 



Synchronizing lamps are often used in connection 
with synchronizers. If the difference in speed be¬ 
tween two generators is great, the instruments do not 
always indicate right, and for this reason the synchro¬ 
nization is started with the lamps and finished off with 
the instrument. In connecting up a synchroscope it 
should always be checked with lamps to see that it 
indicates right. If it does not, some of the wires must 
be changed until it does. 





















































142 


Operating and Testing 


Figure 92 shows the switchboard connections of the 
Westinghouse synchroscope arranged for high poten¬ 
tial. V T are the voltage transformers, one for each 
machine, P the plug receptacles and L the synchroniz¬ 
ing lamps. 

The power factor meter is similar in principle to the 
synchroscope and the switchboard connections for two 
phase are shown in Figure 93, and for three phase in 
Figure 94. If necessary a voltage transformer is cut 
into the circuit, as indicated by dotted lines. Three 




lamps cross connected between the three phases ag 
shown in Figure 95 can also be used for synchronizing 
in connection with three phase circuits. 

Let the two halves of the figure at the right and 
left each represent a dynamo, both of which are to be 
operated together. If both are running at the same 
speed they will be in synchronism and whatever rela¬ 
tion as to brilliancy between the different lamps may 
exist at any moment will exist at all times, i. e., the 
lights will work in unison either up or down. If, 
however, one of the machines is moving faster there 





































Operation of Alternators 


143 


will be a steady change in all of the lights. To get a 
clearer view of this let the machine at the light be 
moving twice as fast as, the one at the left. The 
E.M.F.s of the two machines will then at any time be 
represented by the length of the line measured from 
y J3, either up or down until it intersects the sine 

curves. 

To find the brilliancy of any of the lamps A B C we 
must note the difference of potential between the 



phases to which it is connected. If both E.M.F.s are 
above the horizontal line they must be subtracted, the 
lesser from the greater, if one is above and the other 
below the values must be added, since they represent 
opposite polarities. Following this out we obtain the 
table below in which the numbers stand for relative 
brilliancy, 0 representing darkness and 14 the highest 
obtainable voltage which is double that of one dynamo. 








































































































































































































































































































































144 


Operating and Testing 


The numbers 1, 1, 2 , 2 , etc., indicate the advance in 
speed of one machine over the other, that at the right 
moving twice as fast as the other. 


TABLE A 


1 1-1 

2-2 

3-3 

4-4 

5-5 

6-6 

7-7 | 

8-8 

A 

6 

11 

2 

0 

5 

4 

2 

13 

B 

6 

14 

9 

6 

11 

3 

0 

3 

C 

0 

6 

4 

5 

13 

11 

3 

11 


With conditions as above the lamps will light up in 
the order A, B, C. If the machine at the left moves 
faster than the other the lamps will light up in the 
order C, B, A and thus give an indication as to whether 
the incoming machine is running too fast or too slow. 


















CHAPTER XII 

MOTOR OPERATION 

We have already seen that the ordinary direct cur¬ 
rent motor requires some resistance in the circuit at 
starting to prevent an excessive rush of current during 
the time the armature is developing the necessary 
counter E.M.F. 



One of the best rheostats for this purpose used in 
connection with shunt or compound motors is illus¬ 
trated in Figure 96. This rheostat is equipped with 
‘ 1 o\ erload ’ ’ and ‘ ‘ no voltage ’ ’ releases. Both of these 
are necessary to protect the motor properly but it is 
possible to operate motors without them as the ordi¬ 
nary fuse, if of proper size, will take care of the 
me tor. An overload will cause excessive current to 
pass through the armature and a drop in voltage will 
do the same thing especially if it is sufficient to cause 




145 












146 


Operating and Testing 


the motor to come to rest, in which case the armature 
becomes a short circuit and will rapidly burn out. 

Referring to the diagram, current enters at 1 and 
passes through magnet 2 and the arm A of the rheo¬ 
stat. Here the circuit is open until the arm is moved 
to the right; when the arm touches the first point of 
R current begins to flow through all of the resistance 
and the armature and at the same time through the 
fields. It is important that the conections be so made 
that the field is fully excited before the armature re¬ 
ceives much current as the current will flow through 
the armature much more rapidly than through the 
fields. It will be seen that the field current passes 
through magnet 3 and when the arm is finally brought 
to the last point this magnet engages an iron armature 
on the arm A and thus holds it at that point as long 
as current flows through the magnet. Should the volt¬ 
age of the circuit drop off considerably the magnet 
will be unable to hold the arm and a strong spring 
attached to it will force it back to the off position. 
Should the motor be overloaded the armature of mag¬ 
net 2 will be drawn up and close the circuit at 4; 
this will shunt the current around magnet 3 and cause 
it to release the arm which will then fly back. If 
desired, push buttons or switches can be attached to 
this shunt circuit in the same manner at different 
places, so that the motor can be stopped from any of 
these points. 

Attention is called to the manner of connecting up 
this rheostat; it will be noticed that the field circuit 
is never entirely opened. This is an important feat¬ 
ure as it prevents much of the destructive sparking 




Motor Operation 


147 


which always occurs when a circuit containing electro¬ 
magnets is opened. It also saves the insulation of the 
motor from many very severe strains as a very high 
E.M.F. is developed for an instant when the field cir¬ 
cuit is broken. With this connection this is avoided 
and the field discharge passes through the armature 
which acts as generator through this circuit until it 
comes to rest. If the switch on a motor provided with 
a rheostat as shown is suddenly opened the arm of 
the rheostat will not fly back at once but will be held 
in place by the current generated by the armature for 
a few moments until it comes nearly to rest. 

The rheostat should always be located so that the 
action of the motor can be observed from this place; 
if belting, etc., connected to the motor can be seen 
from the rheostat it will answer the purpose. 

The first step in starting a motor is to close the 
main switch; next move the arm of the starting box 
slowly and note whether the armature begins to move. 
If it does not do so it is not safe to continue movement 
of the arm, but instead it should be returned and the 
cause of the trouble located. (See Motor Troubles.) 

Ordinarily not more than 30 seconds should be con¬ 
sumed in moving the arm from starting position to 
position of rest. If more time is taken the rheostat 
coils are likely to burn out. This of course depends 
very much upon the load the motor may be carrying 
when starting. If the arm is moved over too fast the 
armature is likely to burn out. This also depends 
greatly upon the load it may be carrying at the time. 
During the time of starting and immdeiately after¬ 
ward the condition of the brushes should be noted and 


148 


Operating and Testing 


they should be adjusted to point of least sparking. 
Good modern motors should not spark at all. Motors 
equipped with starting boxes like the above will gen¬ 
erally take care of themselves if for any reason the 
current should fail. If the starting box is not auto¬ 
matic the switch of the motor should be opened at 
once in case the current fails; a sudden coming on of 
the current would either blow fuses or bum out the 
armature. Motors with such starters should also be 
disconnected from the service before the generators 
are shut down at noon or evening. This may be done 
either by the attendant at the motor or by the man in 
charge of the switchboard. In all larger, well man¬ 
aged installations it is customary to have certain men 
detailed to stop and start all motors at the proper 
time. 

Series motors, such as are used on street railways, 
cranes, etc., unless specially wound or used in connec¬ 
tion with a very steady load require constant attention 
and cannot be operated unless an attendant is always 
at hand. 


ALTERNATING CURRENT MOTORS 

Alternating current motors fall into three general 
classes: Single phase induction motors; polyphase in¬ 
duction motors; synchronous motors. The single 
phase induction motor requires some artificial means 
of starting, as illustrated in Figure 63. The direction 
of rotation can be varied by reversing the connections 
of either one of the two windings. 

The smaller of these motors require no starting 
boxes. At starting they draw a very heavy current, 


Motor Operation 149 

usually from 5 to 6 times the running current, but 
this soon ceases. 

With the larger motors up to 5 H.P. the switching 
arrangement shown in Figure 65 may be used. This 
switch is shown three phase but may be used equally 
well with single phase. The switch is thrown to the 
up position and held there until the motor has gained 
considerable speed and the heaviest rush of current is 
over; it is then thrown downward and the motor con¬ 
tinues to run but now under protection of the fuses. 
This throwing over of the switch must be quickly 
done so that the motor will not lose much speed 
in the interval during which it is without current. 

If an induction motor is overloaded it will often 
come completely to rest and burn out. 

The motor most commonly used for power purposes 
is the 3 phase motor. Two phase systems are not 
much used. This motor is self starting and requires 
no help in this respect. But like the single phase 
motor the currents required at starting are very much 
greater than the running current. It is therefore 
customary to use the same starting devices as with sin¬ 
gle phase motors, but as this type of motor is used 
in much larger units than the single phase better 

starting devices are furnished. 

Figure 69 shows a diagram of an auto starter used 
with 3 phase motor. So long as the switch is in the 
position shown the current must pass through the re¬ 
actances 1, 2, 3, and these prevent the heavy rush 
of current which would take place otherwise. After 
the motor has attained nearly its running speed the 


150 


Operating and Testing 


switch is thrown up and the motor receives the full 
line pressure. 

It is always best to arrange such motors so they can 
be started without load. 

With larger sizes of induction motors the rotor is 
often wound. In such cases a resistance may be 
placed in the motor circuit and operated as with direct 
current motors. The resistance may be fully cut out 
when the motor attains full speed (See Figure 68.) 

Three phase motors may be reversed in direction by 
changing the relative position of any two wires leading 
into the motor. 

With all induction motors the efficiency is quite low 
unless the rotor is made with a very small air gap be¬ 
tween it and the stator. A very small amount of 
wear will therefore be likely to bring both in touch 
and ruin the motor. For this reason great care in the 
application of belts must be used; too tight a belt will 
soon wear the journals and allow the rotor to come in 
contact with the stator. 

A three phase motor will not start unless all of the 
wires are delivering current, but it will continue to 
run if one or two of the phases are out of circuit. 
Under these conditions, however, it will draw very 
heavy currents and very likely burn out. 

Polyphase synchronous motors, if there is no other 
way, may be started by allowing current to flow in the 
armature while the field circuit is open. This method 
gives rise to much trouble and is not to be recom¬ 
mended. Such motors should be brought up to speed 
and started like alternators running in parallel. (See 
Synchronizers and Operation of Alternators.) 


CHAPTER XIII 

TRANSFORMERS 

The losses of energy in an electric circuit are pro¬ 
portional to the current flowing. The power trans¬ 
mitted is proportional to the product of the current 
and pressure-amperes and volts. Bearing these two 
facts in mind, we can easily see that to reduce losses to 
a minimum we should work with a minimum current, 
but as we decrease the current we must increase the 
voltage in the same ratio. To transmit a given amount 
of power, if we divide the current by 2, we must multi¬ 
ply the volts by 2. 

High electrical pressure, it is well known, is quite 
dangerous, not only to human life, but there is also 
considerable fire hazard with it and it is furthermore 
impracticable to use it in many places where, for in¬ 
stance, insulation is difficult. This fact again makes 
it desirable to avoid the use of high pressures where it 
is likely that inexperienced humanity may come in 
contact with it. 

In the electric transformer we have the means of 
using electrical pressure at a low potential, if neces¬ 
sary, inside of buildings, increasing that pressure to 
a great extent out of doors and reducing it again to a 
safe potential when we enter the premises where power 

is to be used. 


151 


152 


Operating and Testing 


Since we can raise the pressure to a great extent on 
that part of the line which is pretty well out of reach 
of most people, we need but a correspondingly small 
current and can, therefore, get along with correspond¬ 
ingly small wires. 



Figure 97 


An illustration of such an installation is diagram- 
matically shown in Figure 97. The transformer T 
nearest the dynamo is known as a “step up” and the 
other as a “step down” transformer. A step up 


vwww 
mrnrn 

wmm 

X 

Figure 98 



transformer is not always used, very often the full 
line potential, is generate direct by the dynamo. On 
the other hand, in many cases a double transformation 
is required as illustrated in Figure 98. This only as 












































Transformers 


153 


a safeguard, however, as it has no operating advan¬ 
tages; it merely reduces the liability of breakdown in 
the insulation. 

A complete comprehension of the transformer re¬ 
quires a knowledge of the phenomena of electrical in¬ 
duction and inductance and without this knowledge 
one cannot intelligently operate or test transformers. 
The term “electrical induction’’ describes the induc¬ 
ing of one current by another. We are already some¬ 
what familiar with the phenomenon of lines of force 
cutting wires, but it will do no harm to touch upon 
this subject again. 



Referring to Figure 99, if a current is started in 
one of the closed circuits, A, for instance, it will set 
up lines of force encircling the wire as indicated 
by the arrow, B. These lines of force we know re¬ 
quire power to create and oppose the current which is 
creating them. So long, however, as their only chance 
of action is on the same conductor in which the cur¬ 
rent which gives rise to them flows, their only effect 
is to retard or check the current flow as long as they 
are increasing in number. After they have attained 
a steady value, they no longer retard the current, in 
fact have no further effect on it until they begin to 
decrease in number again. If, however, these lines of 















154 


Operating and Testing 


force are in position to “cut,” i. e., to encircle another 
closed conductor, they at once give rise to currents in 
it and these currents since they are created by a force 
which opposed the original current or force must, of 
course, be in opposition to it. Thus it is that when¬ 
ever two closed conductors are laid side by side and a 
current is set up in either of them, another current 
opposing the first will be set up in the other circuit. 
Thus the first current is said to induce the other and 
is spoken of as an inducting or primary current, while 
the other is known as the induced, or secondary cur¬ 
rent. The phenomenon above referred to is that of 
electrical induction and every change in current 
strength and direction in one such conductor will be 
followed by a corresponding change in tne other. 

We have seen how an electric current induces an¬ 
other current in a neighboring conductor if that con¬ 
ductor is part of a separate coil. Similar induction 
also takes place in wires belonging to the same coil, 
as these are also cut by the same lines of force and as 
this opposes the original current, it gives rise to what 
is known as the counter E.M.F. of self-induction, or 
self induction, or inductance. 

AVe have now a clear view of these two phenomena; 
that the primary coil tends to induce currents in the 
secondary coil and also opposes itself. AA r e have also 
seen in previous chapters that both of these effects are 
largely increased if the wires are wound upon an iroa 
core having high magnetic conductivity. AVith every 
good transformer there is a magnetic circuit of very 
high conductivity, so that the self induction of the 
primary circuit is very great. In fact, it is the aim 


Transformers 


155 


of all builders to make it so great that very little 
current will flow while only the primary coil is con¬ 
nected. 

Now let us examine the effect of the secondary coil. 
We know that the primary coil induces currents in it 
which flow in opposition to those in the primary. Fur¬ 
thermore, it is evident these currents must react upon 
the primary in just the reverse direction that the pri¬ 
mary currents react upon themselves, in other words, 
they tend to lessen the self induction of the primary 
coil and bring about a greater current flow in it. The 
secondary coil also, of course, reacts upon itself, but 
this reaction is again balanced by the greater action 
of the primary. Thus the whole current flow in a 
well designed transformer is governed by the second¬ 
ary coil. If it is an open circuit, no current flows; if 
one light is turned on, there is some flow; if more are 
turned on, the current is in proportion, all of course 
within the range of the carrying capacity of the wires. 
This interaction of the tw T o currents is called “mutual 
induction” and it is this interaction wdiich makes the 
transformer so useful and efficient. 

In practice the electric transformer consists of an 
iron core upon which tw T o separate coils of ware are 

w r ound. 

These two coils must be insulated from each othei, 
but should otherwise be as close together as proper re¬ 
gard for safety will permit. One of the coils of wire 
is usually subject to much higher pressure than the 
other and there is always danger of the insulation be¬ 
tween them breaking down. Many fires and some 
loss of life have been caused bv this. 







156 


Operating and Testing 


In Figure 100 there is shown a diagrammatic illus¬ 
tration of a transformer having a ratio of 10 to 2; by 
this is meant that the number of turns of wire in one 
coil is 5 times as great as in the other; with this ratio 
the voltage in the coil having the most turns will be 
5 times as great as in the other, while in the other the 
current will be 5 times as great as in the first. In 
both coils the power will be the same, if they are 
properly designed; if we neglect the losses due to 
heating hysteresis, etc., which, however, in large well- 
designed transformers, should not be over two or 




three per cent and if they are operated on full load 
even less. 

In order to see more clearly that the power in both 
coils is the same, we must bear in mind that the sec¬ 
ondary coil can deliver no more power than it re¬ 
ceives from the primary and (supposing a transformer 
of 100 per cent efficiency) the primary coil must be 
of such self induction that no current whatever will 
flow as long as the secondary coil is on open circuit. 
Hence the primary can deliver only enough power to 
provide what the secondary is taking and the power 
in the coils must be always the same. 


Transformers 


157 


The losses in the transformer are due: First, to the 
-ohmic resistance of the coils; second, to inefficiency of 
the magnetic circuit provided by the iron core; third, 
to eddy or foucault currents generated in the iron 
oore and also in the copper wires themselves (this is 
very small), and fourth, to hysteresis. 

As transformers grow old, they are very *apt to 
lose in efficiency, although some makers have recently 
produced iron which it is claimed does not deteiiorate 

with age. 



The losses due to ohmic resistance can be reduced by 
using larger wire of higher conductivity. The losses 
due to foucault currents are kept at a minimum by 
“laminating” the iron core of the transformer. Since 
foucault currents are induced by lines of force which 
act at right angles to the inducing current, they must 
flow in the same general directions as the currents 
which produce them, hence, to introduce as much re¬ 
sistance as possible into their circuit (which is the 
iron core) it is built up of thin washers insulated from 
each other, sometimes by thin paper, often by mere y 














































158 


Operating and Testing 


the oxidization on the sides of the plates. The rela¬ 
tive position of wire and plates is shown in Figure 
101; arrow 1 shows direction of inducing current, 
arrow 2, direction of lines of force and arrow 3, direc¬ 
tion foucault currents would take if the insulation 
between the laminations did not prevent them. 

Wvvy wwv wvw 
mtm - mm — -mmm— 


Figure 102 

Transformers are connected in series sometimes, as 
shown in Figure 102. As a rule transformers con¬ 
nected this way are small, each supplying only a few 
lights. 



Figure 103 

The majority of transformers are connected in par¬ 
allel, as illustrated in Figures 103, 104 and 105. 

Figure 103 is the simplest and requires no other 
testing than to determine which is the primary wire. 
This is usually easily determined by simply noting the 
size of the two pairs of wires which project from the 
transformer, the smaller being the primary. Should 























Transformers 


159 


these wires be identical in size, the resistances of the 
two coils should be measured. This can be done with 
a Wheatstone bridge or with a voltmeter, the volt- 


o 


-o 


-o 

-o 


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Figure 104 



meter test being made as shown in diagram, Fig¬ 
ure 106. Use a low potential circuit and direct cur- 



MAAAA 

Figure 106 


rent if possible and allow no one to come in contact 
with the ends of the coils as a very high potential may 
be generated in one of them. 













































160 


Operating and Testing 


The coil having the higher resistance will show the 
lowest reading on voltmeter and may be set down as 
the primary in case of a step down transformer and 
secondary in case of a step up transformer. 


O 

O 

O 


o 

o 

o 





Transformers are often connected so that their sec¬ 
ondaries may operate on the 3-wire system. Figures 
107 and 108 show the right and wrong connections. 
Both methods will operate the lights, but with the 
wrong method the neutral or middle wire will be called 











































Transformers 


161 


upon to carry double current and the loss in the wires 
will probably be excessive. With the right method, 
both transformers will use only as much current as one 
would use, but they will have double voltage, 2 lights 
being in series. This method makes possible a great 
saving in wire. One can easily determine whether 
such a bank of transformers is connected right or 
wrong by connecting two lamps across the two outside 
wires without connecting to the neutral. If the lamps 




mnumm ■ ■ ■ f 

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MWA 



Figure 109 


burn properly the transformers are O K.; if they are 
connected wrong the lights will not burn at all. 

When transformers are banked either in parallel 
or in series it is necessary that their polarity be known. 
With transformers of the same make, it is safe enough 
to assume that all are of the same polarity and to con¬ 
nect them accordingly. If, however, transformers of 
different make are to be run together, they should be 
tested and marked beforehand. To do this make con- 












162 


Operating and'Testing 


nections to some direct current as shown in Figure 
109. A direct current applied to a transformer will 
cause one impulse to be given to the voltmeter or gal¬ 
vanometer shown in the secondary. On each trans¬ 
former mark that wire of the primary which gives a 
certain deflection on the voltmeter and in banking 
these transformers, see that these marked wires all 
connect to the same primary wire for parallel working. 
For this test a voltmeter whose deflections depend 
upon the direction of current must be chosen. 





Figure 110 

In Figure 110 another system of banking transform¬ 
ers is shown that often leads to trouble. If the prb 
mary fuse in one transformer “blows,” it is evident 
that current from the other transformers will circu¬ 
late in the secondary and thus add the transformer 
to the load in lights they have to carry, thus shortly 
causing other fuses to blow. Small transformers are 
far less efficient than large ones and this connection 
should not he used when it can be avoided. 

Transformers to operate with a given voltage and 
frequency must be designed for this. If a higher 


















Trans formers 


163 


frequency is employed than the transformer is de¬ 
signed for, its self-induction will be too great to per¬ 
mit current flow. If the frequency is less than called 
for by the transformer, it will generate excessive volt- 


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age and overheat the transformer unless fuses are 


blown. 

Two transformers of the proper frequency, but only 
one-half the voltage of the circuit may be operated 
in series ,in either of the ways shown in Figures 111 
and 112. 


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2 

MAMMAAT 

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Figure 113 



Figures 113 and 114 shows methods of connecting 
three-phase transformers. Figure 113 shoe's what is 
termed the delta connection and Figure 114 the Y or 
star connection. The delta connection has the ad¬ 
vantage that the burning out of one transformer does 























































164 


Operating and Testing 


not seriously affect the operation of the other two, and 
even when two transformers fail the third will still 
operate on one phase. This is not the case with the 
star connection, one transformer failing seriously 
hampers the whole group. 

Figure 115 is drawn to illustrate the voltage or cur¬ 
rent relations existing between star and delta con¬ 
nected transformers. S represents the star, and D the 



delta connection. Suppose the current be as shown 
by the curves under 1 at the left. At this instant 
phase A is at zero, and B is negative and equal to C 
positive. This leaves SI without current for an in¬ 
stant and S2 and 3 in series taking the voltage of two 
phases. Between 3 and 4 A has risen to its maximum 
positive and B and C are negative and equal. The 
total current now passes through SI and divides 
equally on the return through S2 and 3. At 5 A and 












































































Transformers 


165 


B are both positive and C is at a maximum negative, 
thus taking all of the current coming through SI and 
2 through S3. The above relation of the current in 
the different phases will hold for all intermediate po¬ 
sitions and it can be seen that at no time is any on© 
transformer coil subject to more than the current of 
one phase. 

If we take up the delta connection in the same way 
we shall notice that at 1 coil D3 is subject singly to 
the pressure of two phases. There being no pressure 
at A, at this point current is also passing through D1 
and 2 in series. 



Figure 116 


A complete investigation of this shows that with a 
given circuit for star connection the individual trans¬ 
formers are subject to only .58 of the voltage between 
the phases necessary, or for transformers to be used 
with the delta connection. If the same transformers 
used for star are connected delta, the current required 
for the delivery of a certain amount of power will be 
1.73 times as great for the delta connection as for the 
star. While many transformers are so built as to be 
serviceable on either connection, it will not be safe to 
assume that all of them are and the operator should 
first inform himself on this point. 

Figure 116 shows the methods of connecting up 
distributed transformers on three-phase circuits. The 












166 


Operating and Testing 


three heavy lines denote the three-phase wires which 
carry the main current and the light line denotes a 
fourth wire used for balancing. This wire may be 
run all the way from the generators or may run only 
between the different transformers This wire is nec¬ 
essary when a number of transformers located some 
distance apart are to be connected star, but is not 
needed for delta connection. It is also not generally 
used where a bank of transformers are feeding a lot 
of motors or a big installation of lights. Whether the 
transformers are connected star or delta, or whether 
they are located close together or long distance 


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Figure 117 


Figure 118 


apart, it is always important to arrange so that the 
load may be as evenly as possible divided between the 
different phases. 

In some instances, to save the cost of one transformer, 

three-phase transformers are connected as shown in 

Figure 117. Many transformers are wound so they 

can be used with different voltages and current. The 

manner in which this is effected is illustrated in Fig- 

© 

ure 118. If the ends A B and C D are joined the 
transformer-windings are fitted for but half the volt¬ 
age but double the current as could be used if C were 
joined to B. This latter connection places windings 


























Transformers 


167 


in series, while the former places them in parallel. In 
connecting two such coils in series care must be taken 
that current passes through both in the proper direc¬ 
tion, if the connection should be made A C D B one- 
ha if of the transformer would oppose the other. 

As it often happens that the insulation between the 
primary and secondary wires gives way and thus great 
danger to life and property results, it is advisable to 
ground transformers, as illustrated in Figure 105, the 
ground wire C being connected to some neutral point 
on transformer. The shells of all transformers should 
be grounded. 

The principal losses in a transformer are the core 
losses, due to inefficiency of magnetic circuit, and the 
copper losses due to the ohmic resistance of the cop¬ 
per. 

The efficiency of a transformer can be determined 
by measuring the power supplied to the primary by a 
watt-meter and dividing the power obtained from the 
secondary by it. 

The core losses can be determined by measuring the 
current flowing in the primary while the secondary is 
open and noting the percentage of this current to the 
maximum current. 

The copper losses are found by short circuiting the 
secondary winding and applying voltage enough to 
the primary to cause the full load current in the sec¬ 
ondary. The greater the copper resistance, the more 
power must be supplied to the primaries. This power 
must also be measured with a wattmeter. Volt and 
ammeter measurements cannot be used with altemaf- 


168 


Operating and Testing 


ing currents. This method is due to Dr. Sumpner, and 
connections are shown in Figure 119. 

Every transformer before being connected should 
be tested for insulation between the two coils and each 
coil for insulation from the shell, as well as for conti¬ 
nuity. These tests can all be made with a wheatstone 
bridge. 

As high potential is nearly always used in connec¬ 
tion with transformers, great care is necessary in 



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Figure 119 


handling them. The following rules should be care¬ 
fully observed: 

Do not handle more than one wire at a time, and 
touch it only with one hand at a time. 

Wear rubber gloves and do not let them be moist. 

Keep yourself insulated from the ground and from 
all other wires. 

'Do not place fuses in circuit until all connections 
have been made. 

























7 vans formers 


169 


Use enclosed fuses; a small rubber tube over the 
fuse wires is better than nothing. 

If working on a line that is “dead,” treat it as 
though alive. It may be “thrown in” at any moment. 

Take no chances, protect yourself by short circuit¬ 
ing and grounding the line. 

Be very careful not to part wires, keeping one end 
in each hand; you will cut yourself into the circuit. 

With old transformers especially, and with all traps 
formers that are not grounded, treat the secondaries 
as you would the primaries. 


CHAPTER XIV 




BATTERIES—PRIMARY BATTERIES 

The term, battery, is applied to a number of cells 
grouped together either in series or in parallel. It 
should never be applied to a single cell. Batteries may 
be grouped according to any of the methods shown in 


I I I I — 



Figure 120 

Figure 120. For all ordinary work, the method at the 
top is employed. The voltage of this arrangement is 
four times as great as that of a single cell. 

If the same number of cells be grouped as in the 
center of the figure, the voltage will be but two times 










Batteries 


171 


that of one cell, but the current obtainable will be 
twice that of the above. With the arrangement at the 
bottom, the voltage will be equal to that of one cell, 
and the current obtainable four times as great as that 
from the first figure. The voltage of a number of cells 
in series is equal to the voltage of one cell multiplied 
by the number of cells. 

The voltage obtainable from any cell is independ¬ 
ent of its size or of the distance apart of the plates. 
In any given cell, however, the current obtainable is 
proportional to the size of the plates opposed to each 
other in the solution, and inversely as their distance 
apart. The distance apart of the plates affects the 
current only, as it increases the resistance. 

The fall of potential when current is flowing is pro- 
portional to the product of the resistance of the bat¬ 
tery or cell and the current in amperes. If the bat¬ 
tery has a high internal resistance therefor, the drop 
in voltage will be quite great when much current is 

taken from it. 

A battery is placed to the best advantage when the 
cells are so arranged that their resistance is nearest 
equal to that of the line through which they are work¬ 
ing. If the resistance of the line or instruments is 
greater than that of the battery all of the cells should 
be placed in series; if the external resistance is less 
than that of the battery, the cells should be arranged 
in multiple until their resistance becomes as low as 

that of the line. . . , 

The resistance of a number of cells m series is equa 

to the resistance of one cell multiplied by the tota 
number of cells. 


] 72 


Operating and Testing 


The resistance of a number of cells in parallel is 
equal to the total resistance of one of the series groups 
divided by the number of sets in parallel. 

Primary batteries are divided into two classes; one 
of these is suitable for continuous work only, and will 
rapidly deteriorate unless kept at work. The other 
will very quickly run down when kept in continuous 
use. 

The best known of the continuous current type is 
the “gravity cell.” In this cell the positive pole con- 



Figure 121 


sists of copper located at the bottom of the jar as 
shown in Figure 121, and the negative of zinc ar¬ 
ranged at the top, as shown. Both of the elements 
are immersed in a solution of sulphate of copper com¬ 
monly spoken of as “ blue stone. ’ ’ This type is suit¬ 
able only for such work as telegraphy, where very 
small currents are used. The internal resistance of 
this cell is very high. 

The open circuit batteries are far more in use and 
exist in many forms and include nearly all of the dif¬ 
ferent makes of dry batteries. Aside from dry bat- 









Batteries 


173 


teries, the most notable kind is the Leclanche. In this 
cell the positive pole is of carbon immersed in a solu¬ 
tion of sal-ammoniac, and the negative pole is a piece 
of zinc immersed in the same liquid, but insulated 
from the carbon. This cell as well as the different 
kinds of dry batteries, are capable of delivering a 
strong current for a short time. If left in circuit, 
however, in a few minutes they will run down so tha* 
no current can be obtained. No matter, however, hov 
badly such a cell may be run down in time it will 
often recuperate. These cells are universally used 
for bell and telephone work and consume no energy 
when not in use. 

If the following directions are carefully observed 

little trouble will be experienced, 

Leclanche and similar open circuit batteries. 

Use no more salomoniac than will readily dissolve. 
Five or six ounces is the quantity required for ordi¬ 
nary cells. 

Do not fill jar more than three-fourths full of water 
and keep it in a cool place to prevent evaporation. 

See that water does not freeze. 

Remove such zincs as become coated with crystals. 
They are impure and introduce very high resistance 

in the circuit. 

Remove carbons and let them dry out occasionally. 
Do not allow battery to be in use very long at one 

time. , 

Do not allow it to become short circuited. 

If battery has been short circuited disconnect it 
and it will often pick up again. 




174 


Operating and Testing 


CLOSED CIRCUIT BATTERY—GRAVITY CELL 

Fill jar nearly full of water and throw in sufficient 
sulphate of copper (blue vitriol) to give a slight blue 
color to about half of the water. The blue part of the 
solution will be the heavier and will settle at the bot¬ 
tom. Enough should be provided so that the dividing 
line will be maintained about half way between the 
zinc and the copper. 

To start the action of this battery it may be short 
circuited for a while; it must never be left on open 
circuit for any great length of time. 

ACCUMULATORS OR STORAGE BATTERIES 

Storage batteries are used in connection with iso¬ 
lated or central stations, to supply current w T hen the 
dynamos are not running, as well as at the hours of 
heaviest load when perhaps the capacity of the dy¬ 
namos may not be fully equal to the demands made 
upon them. 

It must be borne in mind that it is not customary 
to provide dynamo capacity for all of the lights and 
power connected to the system, the assumption being 
that seldom more than 25 to 50 per cent of the con¬ 
nected load will be used at any one time. If a suita¬ 
ble storage battery is connected to the system, the 
dynamo capacity may be even less, for the battery 
can be charged during the slack hours when but very 
little current is being used for other purposes. Thus, 
if properly arranged, the dynamos and engines can 
be kept working at their full capacity and highest 
efficiency most of the time. 


Batteries 


175 


The plates of the cell are of lead (See Fig. 122) 
and there is always one more negative plate than 
there is of the positive. These plates are usually con¬ 
tained in glass or porcelain jars for the smaller sizes 
and for the larger portable batteries of hard rubber. 
The cells for very large permanent installations are 
often made up of heavy planking lined with lead. 

The positive plate always contains the “formation 
which may be either mechanically applied, or 



Figure 122 


“formed” by the action of the charging current. 
Those batteries in which the active material is applied 
in the form of a paste are generally known as the 
Faure typo, while those in which the active material 
is produced by charging and discharging are known 

as the Plante type. . , 

The electrolyte used in connection with these bat¬ 
teries is always sulphuric acid diluted to a specific 
gravity, averaging about 1.20. The acid should be 























































176 


Operating and Testing 


pure and the water used should be distilled. The 
battery room should be well ventilated and all iron 
work should be covered with water proof paint. 
AVooden floors should not be used. Cement floors are 
best. 

The cells should be well insulated and the specifi¬ 
cations of the National Electrical Code should be fol¬ 
lowed in this respect. 

The cells are connected with the positive pole of 
one to the negative of the other, just as an ordinary 
battery, and they may also be connected in multiple. 
Connection in multiple, however, has no advantage 
that can not much better be obtained by procuring 
larger cells and is, therefore, very seldom practiced. 

The E.M.F. of a cell fully charged is about 2 x /2 
volts, and should not be carried much beyond this. 
AVhen the cell is overcharged oxygen and hydrogen 
gas are given off. The E.M.F. should not be allowed 
to fall below 1.8 volts under any circumstances and 
the nearer at full charge the battery can be kept the 
better it is. On no account should any battery ever 
be left standing without charge, and the electrolyte 
should never be applied unless everything is in read¬ 
iness for immediate charging. 

The connections from one cell to another had better 
be soldered or welded so as to leave no chance for 
loose connection. 

As the water evaporates, it must be from time to 
time replenished. This is best done with a hose 
which may lead the water into the bottom of the jar 
where otherwise the heaviest part of the solution will 
concentrate. 


Batteries 


177 


In handling water and acid, never pour water into 
acid; always pour the acid into the water. Much 
heat is generated when the two are mixed. 

Every cell should be tested quite frequently with 
voltmeter and hydrometer. The best indications of 
the condition of a cell are obtained by hydrometer 
tests. 

If the voltage of one cell is much lower than that 
of the others, the cause will often be found to be a 
short circuit of some kind in the cell. 

To charge storage batteries it is necessary that the 
current pass into the battery in the opposite direc¬ 
tion that current flows from the battery when in use. 

In most cases it is necessary to charge the battery 
to a higher potential than that at which the dynamo 
operates. This cannot be done unless a booster of 
some kind is employed. A “booster’’ is merely a 
generator through which the total current passing 
into the battery flows and in which a certain addition 

to the voltage of the circuit is made. 

Figure 123 shows the connections of a compound 
dynamo used to supply current to the bus bars, and 
also to charge a storage battery. In this figure B is a 
belt driven booster, through which all current pass¬ 
ing from the dynamo into the battery must pass and 
in which the pressure can be raised the desired 
amount. This booster is provided with fields like an 
ordinary dynamo, and the field strength can be ad¬ 
justed. To charge, the double throw switch S is 
thrown upward and current now passes from the plus 
pole of the dynamo to switch S, then along wire C to 
the main cells of the battery and through the battery 



178 


Operating and Testing 


ammeter, the booster the other pole of switch S and 
the minus pole of the dynamo. 

To discharge, the switch is thrown downward and 
current now passes in the reverse direction to the bus 



bars, leaving the booster out of circuit The discharge 
current, however, must pass through the cells con¬ 
nected at R. In the above case, these are simple lead 
plates known as counter E.M.F. cells and oppose the 
flow of current so that by their aid the rate of dis- 



















































































































Batteries 


179 


charge can be controlled. As the battery discharges 
and its E.M.F. falls more and'more of the cells are 
cut out. Very often the method of regulation is by 
means of end cells which are charged at the same time 
as the battery. In such a case the connections must 
be as indicated by dotted lines and wire C, as the 
E.M.F. of the battery falls, more and more of the end 
cells are cut into the circuit and their E.M.F. added 
to that of the battery 


+ 


hi 


l 



u 








I 



4 


Figure 124 


A method of arranging a storage battery so that it 
can be charged without the use of a booster is shown 
in Figure 124. This battery is arranged so it can be 
charged in parallel, and for this purpose is divided 
into two parts. When arranged for charge the two 
switches in the upper center are thrown downward 
and all of the end cells are cut into the circuit so they 
will be included in the charge. Current now passes 


































































180 


Operating and Testing 


from the positive pole of the circuit through all of 
the resistance R, and the switch S to the two halves 
of the battery. As the counter E.M.F. of the bat¬ 
tery develops resistance is cut out of the circuit by 
closing the switches connected to the resistance, begin¬ 
ning at the right, one at a time and as fast as it ap¬ 
pears necessary. Closing the last of these switches 
at the left cuts out all resistance. Two ammeters are 
provided so the current in both sides can be watched. 

Ordinarily this battery “floats” in the system and 
when arranged for work upper switch S is opened and 
lower switch S is closed. With this connection the bat¬ 
tery will feed into the line whenever the pressure of the 
line falls below the normal and take current from the 
line when the pressure is normal or above. Double 
scale ammeters should be used. They will show 
whether the battery is receiving or sending current. 

When storage batteries are to be charged from al¬ 
ternating current lines, the Cooper-Hewitt Mercury 
Rectifier may be used. 

This mercury alternating current rectifier consists 
of a glass bulb fitted with four electrodes. Two of 
these are of graphite and two of mercury. The mer¬ 
cury electrode will not allow a negative current to pass 
through into the vapor in the bulb, but does not resist 
the flow of current from a positive source into itself, 
if that current has been once established. In order 
to start the flow of current from the positive elec¬ 
trodes P into the mercury electrode N it is necessary 
to establish a metallic circuit from P to N and when 
now this circuit is interrupted the current will con¬ 
tinue to flow into the mercury from the vapor in the 














Batteries 


181 


bulb, so long as the current flow is not broken else¬ 
where. If for any reason the current flow ceases, it 
cannot again be started until the metallic circuit has 
again been established. 

The operation of the rectifier can perhaps be best 
understood by reference to the Figure 125. In this 



figure, A C is the source of the alternating current 
which is to be rectified for the purpose of charging 
the battery. The current passes from whichever side 
of A C may be positive to the positive electrodes P. 
So long as the bulb B remains in its upright position 
no current will flow from P into N. In order to start 
the flow it is necessary to tip the bulb a little to the 





























182 


Operating and Testing 


left so that the mercury in the bottom connects N and 
S. This starts current flow through the starting re¬ 
sistance R, and when the bulb is returned to the up¬ 
right position the current continues; but not from S 


but from P. No current can pass from the mercury 
to the vapor, but there is no hindrance to current flow 
from the vapor to the mercury, provided it has been 
started. As the arc lamp maintains itself through the 
vapor formed by the arc, so the current there main¬ 
tains itself when started through the vapor. Should, 
however, only for an instant the current flow be in- 



Figure 126 


terrupted the bulb would have to be tilted again. It 
will be seen from the figure that each side of the A C 
has an electrode at P, and one of these is always posi¬ 
tive and from whichever is positive the current flows 
into the mercury. 

A reactance E is cut into the circuit which causes 
the current to continue after the E.M.F. has fallen 
to zero until the current at the other side has attained 
some value so that the flow is continuous. 

Storage battery circuits are usually equipped with 
overload and underload circuit breakers, which pre- 








































Batteries 


183 


vent charging at too great a rate and also a reversal 
of the battery current through the dynamo. 

Small batteries for use in connection with bell or 
telephone work are best connected for charging as 
shown in Figure 126, one battery being connected to 
the work while the other is charging. This makes it 
impossible to bring the high voltage dynamo current 
in contact with the bell wiring which, as a rule, is not 
safe for such pressures. The rate of charge can be 
governed by using more or less lamps of different c. p. 
in the sockets indicated at the right of the figure. 




Figures 127 and 128 illustrate other uses for stor¬ 
age batteries. These figures show the elementary 
connections of batteries used in a manner similar to 
compensators. It is here made possible by their use to 
obtain two voltages from one dynamo. 

There are so many different types of storage batter¬ 
ies and so many different sizes that it is impracticable 
to give detailed directions concerning their use. Di¬ 
rections pertaining to any particular battery had best 
be obtained from the maker. 




























































CHAPTER XV 


ARC LAMPS 

If we take two suitable pieces of carbon and con¬ 
nect them to a source of electricity and then bring the 
ends together we shall, of course, obtain a current 
flow through them. If the contact between the two 
carbons is not very good, the current will make itself 
manifest by the heating of the small contact surface 
to redness. If we now slowly separate these points the 
current will continue to flow through the intervening 
air space, forming what is known as the electric or 
voltaic arc. Where the separation is small the cur¬ 
rent will be quite strong and a hissing or frying sound 
will be given out. An arc of this character is gener¬ 
ally spoken of as a low tension, or short arc and re¬ 
quires about 25 volts, and, for successful operation, 
very hard carbons. This type of arc is at the present 
time very little used for lighting purposes. 

If we continue to_separate the carbon points the 
light becomes very unsteady and flickers considerably 
until at a certain point it begins to improve and we 
obtain the long, quiet arc. It will now be found that 
the carbons are separated about y 8 of an inch. By 
measuring the difference of potential across this arc 
we shall find from about 45 to 50 volts and this is the 


184 


Arc Lamps 


185 


proper voltage for open arcs. If we continue to in¬ 
crease the separation of the carbons, the arc will grow 
longer and become decidedly flaming until finally the 
separation becomes too great and the arc breaks. 

The resistance of the arc is very nearly proportional 
to the cross section of the carbons and increases with 
an increased separation of the carbon points. The 
drop in voltage across the arc is not entirely propor¬ 
tional to this resistance, but is also due to a peculiar¬ 
ity of the arc which causes it to act as though a coun¬ 
ter E.M.F. was set up in it. 

The temperature of the arc is very high, about 3500° 
Centigrade, and there is nothing that can withstand 
it. By its help we can drill through the hardest steel 
or rock or the most effective insulation with equal 
ease so that, so far, it has been found impossible to 

construct anything that can resist it. 

The light of a strong arc is very injurious to the 
eyes and has often caused considerable distress and 
even temporary blindness. This is especially the case 
where an arc of two or three hundred amperes is used, 
as for instance, in the drilling of iron beams, or in 
electric furnaces where upward of 10,000 amperes are 
sometimes used. Under all circumstances it is best 
to view the arc through darkened glasses, although 
the ordinary ten ampere arc will not injure the eye 
unless it is exposed to the light very long. 

The length of the arc, or the space between the car¬ 
bons, varies from 1/32 of an inch to one inch After 
a lamp has burned for some time, the carbons will be 
found to have assumed the shape shown in Figure 
12i). It will be noticed that the upper, or positive, 



186 


Operating and Testing 


carbon has been burned in the form of a crater while 
the lower carbon has been burned to a point. The 
crater formed in the upper carbon acts as a reflector 
and it is from this point that the greatest amount of 
light, or about 80 per cent of the total light of the arc, 
is emitted For this reason the positive carbon always 
occupies the upper position unless, for special rea¬ 
sons, it is desired to throw the greater proportion of 
the light in an upward direction. It will also be found 
that the positive carbon burns away about twice as 
rapidly as the negative carbon. The rapid consump- 



Figure 129 

tion of the upper carbon is due to the volatilization 
of the carbon at the crater, considerable vapor being 
formed at this point which is carried across the arc 
and condensed on the negative carbon. 

If, when the arc lamp is burning in its normal con¬ 
dition, the carbons are separated, it will be found that 
the upper carbon is heated for a greater distance back 
from the point than the negative carbon, and it will 
take longer to cool off. This fact, and the nature of 
the shadows cast, forms an easy and practical method 
of determining whether or not, to use the language 
of the lamp trimmer, the arc is burning right or is 



Arc Lamps 


187 


burning “upside down.” When the arc is burning 
with a long separation of the carbon points, the cra¬ 
ter almost wholly disappears and the carbons become 
rounded off. 

When arc lamps are used on alternating current cir¬ 
cuits a voltage of about 28 is used and the current 
must be correspondingly increased. Each carbon be¬ 
comes alternately positive and negative and the two 
carbons burn to points and are consumed at about 
the same rate, the difference in consumption between 
the upper and lower carbon being due to the fact that 
the heat from the lower carbon rises and increases the 
carbon consumption of the upper carbon slightly. The 
alternating current are is much noisier than the direct 
current arc for all ordinary frequencies, but 'with 
very high frequencies this noise ceases. Many lamps 
cannot be operated on low frequencies such as 25 cy¬ 
cles per second. It is not practicable to operate any 
of them much below 25 cycles, as the interval during 
which the current practically ceases becomes of such 
length that the vapor between the carbon points cools 
off sufficiently to entirely interrupt the current. 

Any arc light is affected by strong drafts of air. 
This will often literally blow out the arc and cause 
rapid feeding and short arcs which in turn bring about, 
very rapid consumption of the carbons. A magnet 
applied to the arc also has the effect of blowing it out 
and this fact is often made use of in lightning arrest¬ 
ers and in connection with some arc machines where 
the commutator design is such that severe sparking 

ensues. 

While some of the light of the arc is emitted from 


188 


Operating and Testing 


the arc itself, it is, especially in open arcs, but a very 
small proportion of the total light. Most of the light 
is given out from the carbon points and the quality 
of the carbon therefore has a great influence on the 
character of the light If a poor carbon is used, the 
arc rotates about the carbon, this effect being more 
noticeable when large carbons are used. Impurities 
in the carbon will also cause the arc to constantly 
vary its position and more or less spluttering will oc¬ 
cur, accompanied by a constant change in the color 
of the light. 

As a rule, the best carbon is the one that has the 
greatest range from the point of hissing to the point 
of flaming. With any given carbon these two points 
vary with the length of the arc. If the arc runs too 
short w T e have the hissing sound, when the arc runs 
too long it is the flaming that annoys us. It is evi¬ 
dent that if carbons can be found to bum without 
hissing or flaming over a long range, we need not 
be near so careful with the adjustment of the lamp. 
As this long range of carbons varies also with their 
purity, the test for range is also a good test for the 
light giving qualities of the carbon. As a rule, the 
greater the range of any carbon the more serviceable 
it is. 

The test for range as usually carried out is made in 
the following manner: Insert the carbons to be tested 
in a hand feed lamp. Let them bum with a normal 
current until they have established the proper points. 
Now feed them together slowly until the hissing point 
is reached, and note the voltage across the arc (not 
the whole lamp). Next, separate the carbons slowly 


Arc Lamps 


189 


until they begin to flame, and note this voltage. As 
has been stated before, the greater the range of volt¬ 
age through which the carbons can be operated, the 
better they are. The hissing point is usually about 42 
volts, and the flaming point about 62 volts. 

To test the comparative life of carbons, it is neces¬ 
sary to observe the quantity consumed by a given 
current and voltage in a given time. This is best done 
by arranging that the same current, at the same volt¬ 
age, shall pass through each arc lamp. Then by weigh¬ 
ing, before and after burning, the exact amount of 
carbon consumed in a given time can be ascertained 
The approximate useful life of a carbon can be easily 
determined by burning it for a stated time and ob¬ 
serving the amount consumed. The length of the t ar- 
bon available for burning (not the whole carbon), 
divided by the length consumed in a given time will 
give the approximate life of the carbon. 

The resistance of- carbons is of importance in two 
ways: first, it consumes energy and, second, some of 
the forced, high-resistance carbons do not easily strike 
an arc, i. e., do not volatilize readily enough. The re¬ 
sistance may be measured either with a "Wheat¬ 
stone bridge or with a voltmeter as explained in the 
chapter on testing. In order to reduce the resistance 
of the carbons, they are sometimes coated with copper. 
This will also prolong their life somewhat. Copper 
coated carbons are more generally used for outside 
lighting and should never be used on inside lamps 
unless the arc is entirely enclosed, as hot pieces of cop¬ 
per are thrown off. Another method of reducing the 
resistance of the carbons is to provide a wire or strip 




190 


Operating and Testing 


of metal running through the length of the carbon 
rod. This scheme is made use of in the flaming arcs 
where long carbons of small cross section are used. 

Cored carbons can be burned at a lower voltage 
and, if used in conjunction with solid negative car¬ 
bons will, on direct current, give a very steady arc. 
The soft core being in the center of the carbon allows 
that part of the carbon to burn away faster and thus 
maintain the crater and the arc in one position. Metal 
electrodes are used in some forms of lamps, various 
advantages being claimed for them. They always form 
the negative electrode for, if used on the positive side 
they are very rapidly consumed. 

While there is no definite relation between the size 
of the carbon and the current, it is evident that there 
are conditions which must limit us from either ex¬ 
treme. If a small carbon were used with a large cur¬ 
rent, considerable hissing would result, and the carbon 
would be rapidly consumed, while with a large carbon 
and a small current the arc would rotate around the 
carbon and the light would be very unsteady. The 
carbon points would not be heated to any great extent 
and the efficiency would be low. The size of the car¬ 
bon rods and an outline of the general practice is given 
in the following table: 


Arc Lamps 


191 


ENCLOSED ARC 


Volts 

Amp. 

Upper 

Lower 

15-80 

to 

5 

12 in, x £ in. 

l in. x \ in. 

80 

3 

12 in. x jj in. 

6 in. x | in. 


OPEN ARC 


Volts 

Amp. 

Upper 

Lower 

45 

9.6 

11 in. x | in. 

8 in. x £ in. 

to 


50 

6.8 

12 in. x j S in. 

1 in. x x 7 s in. 


HAND FEED 


Volts 

Amp, 

Upper. 

Lower 

45 

5-10 

6 in. x t t b in. 

6 in. x j 7 b in. 

to 




50 

25-30 

6 in. x l in. 

6 in. x £ in. 


Arc lamps are generally rated according to candle 
power. This is a very much abused and misunder¬ 
stood method of rating. It is evident from an exami¬ 
nation of Figure 130 that the candlepower of the arc 
will depend upon the position from which the meas¬ 
urement of the candlepower is made. Figure 130 
will give a general idea of the manner in which this 
candlepower varies in the case of the ordinary direct 
current arc. The greatest amount of light is given 
out at an angle of about 45° with the horizon. Di¬ 
rectly above and below the lamp the candlepower is 
practically nothing, for, in these positions, shadows 
are cast by the lamp frame. The relative candlepow- 
ers at other positions are shown by the length of the 
radial lines from the center'to the curve in the figure. 

With alternating current arcs the carbons are al- 




































192 


Operating and Testing 


ternately positive and negative, and the distribution 
of light is somewhat different from that of the direct 
current lamp. The maximum candlepower for an arc 
consuming the same amount of current is less with 
an alternating current than with a direct current and 



Figure 130 


the maximum light is thrown out at different angles. 
Figure 131 shows the distribution of light from an 
open, alternating current arc. It will be seen that 
there are two points of maximum candlepower, one at 
40° below the horizontal and the other at 40° above 
the horizontal. 








Arc Lamps 


193 


It is evident from the foregoing description that, 
to compare the light given out by arc lamps it would 
be necessary to take into consideration the light given 
out at all angles above and below the horizontal. This 
is known as the mean spherical candlepower, and is 
obtained by taking candlepower readings around the 
half circle as shown in Figure 130 or Figure 131, and 
taking the mean. This is given as about one-third the 



Figure 131 


maximum candlepower. For a lamp with a maximum 
candlepower of 2,000, the mean spherical candlepower 
would be about 660. The accurate determination of 
the mean spherical candlepower is a rather difficult 
procedure and requires the use of special apparatus. 

A better method of rating arc lamps now in gen¬ 
eral use is the wattage rating. The average wattage 
rating of the various standard lamps is as follows: 






194 


Operating and Testing 


9.6 amps., 50 volts, 2000 nominal c. p., 480 watts. 

6.8 amps., 50 volts, 1200 nominal c. p., 340 watts. 

The proper placing of arc lamps for a given illumi¬ 
nation will depend upon the amount of light required. 
According to many authorities, an expenditure of V 2 
watt per square foot will give medium illumination 
such as is used in train sheds while the most brilliant 
illumination called for can be obtained with 2 watts 
per square foot. This corresponds to approximately 
the distances apart as given in the following table: 


TABLE B 


Medium Illumination 


Brilliant Illumination 

Distance 

Apart 

Height 

Distance 

Apart 

Height 

22 feet 1 10 to 15 feet 
80 feet | 15 to 20 feet 

(3 amp. enclosed arcs.) 
(6 amp. enclosed arcs.) 

12 feet 
21 feet 

10 feet 

12 to 15 feet 


The higher lamps are hung, the evener will be the illumination. 


As a general rule, it is accepted that the distance 
apart of arc lamps should not be greater than six: 
times their height above the floor. Actual practice, 
however, hr many instances varies widely from this 
and often the distance apart is 10 or 15 times the 
height of the lamp, while in other cases only two or 
three times the height is taken as the distance apart. 

With a direct current arc lamp the maximum light 
is given out at an angle of 45° below the horizontal 
and very little light ic: given out in an upward direc¬ 
tion. It is evident that a circular area at a distance 
from the pole equal to the height of the lamp will be 
very brightly illuminated, and, as we move away from 
this position the illumination rapidly diminishes. The 
alternating current arc gives a different distribution 
of light, the maximum amount of light being given 

















Arc Lamps 


195 


out at angles of 40° above and below the horizontal. 
By the use of properly designed reflectors, the light 
which is given off in an upward direction may be so 
reflected as to greatly increase the illumination over 
an extended area and at the same time the bright band 
of light close to the lamp which is present in the case 



Figure 132 


of a direct current lamp is done away with, (See 
Figure 132.) It is in a measure due to this better 
distribution of light that the alternating current has 
come into such general use. 

In order to start any arc lamp it is necessary first 
to bring the carbons together, so that the current can 












196 


Operating and Testing 


flow through them and then to separate them to a 
fixed distance so that the current will be forced to flow 
through the space separating the carbons and thus 
produce the arc. There are two general conditions 
under which this action may take place; one is that 
of a large number of lamps connected in series, the 
same current passing through each and the voltage 
being increased or decreased in proportion as the num¬ 
ber of lamps is increased or decreased. The other is 
that of a single lamp being independently placed in 
circuit in multiple with other lamps or whatever other 
devices there may be connected. In the first case each 
lamp must be equipped with means whereby, should 
its carbons be burned out or the lamp mechanism oth¬ 
erwise deranged so that current does not flow through 
the carbons, the current will be automatically shunted 
around this lamp and continue to feed the balance of 
the lamps in the circuit, so that only the lamp that is 
out of order will be left dark. 

With the other type of lamp this device is not nec¬ 
essary, because the lamp burns independently of all 
others and whenever it is out of order there are no 
other lamps dependent on this circuit for current. As, 
however, when the carbons are brought in contact the 
resistance of the lamp circuit is very low, there is 
likely to be an enormous rush of current through the 
lamp unless some means of checking it is provided. 
For this reason every lamp working on an independ¬ 
ent circuit must be provided with a resistance cut in 
series with it which will keep the current from becom¬ 
ing too g r eat while the lamp feeds or the carbons re¬ 
main together. 



Arc Lamps 


197 


In connection with alternating current lamps the 
same observations apply with the difference that here, 
instead of a resistance, a reactance is used. The 
magnet cores are always laminated to reduce the loss 
and heat due to foucault currents. 

The open arc lamp has a number of objectionable 
features which are causing it to rapidly pass out of 
use. Owing to the fact that the arc is open this type 
of lamp is more or less of a hazard when used in prox¬ 
imity to inflammable material. Sparks of hot carbon 
are thrown off and, if copper coated carbons are used, 
hot copper is also throwm off. If the lamp is used for 
inside lighting, such as in a store, for instance, it is 
absolutely essential that some form of spark arrester 
be provided. An open arc operates satisfactorily only 
at from 45 to 50 volts, so that if it is desired to use a 
lamp of this kind on a 110-volt circuit, a resistance 
must be provided to reduce the voltage to this amount. 
This resistance will, of course, consume as much or 
more energy than the lamp itself, this energy being 
practically wasted. While two lamps could be oper¬ 
ated in series on a 110-volt circuit, this method has not 
given the satisfaction desired. The open arc must 
be trimmed, or provided with new carbons, about ev¬ 
ery 8 to 16 hours, depending on the style of lamp 
used, and, if the arc is exposed to the weather, they 
are more or less affected by the wind, a strong wind 
often blowing the arc out. 

All of these objectionable features are overcome in 
the “enclosed” arc where the carbons, or that part 
of them in the vicinity of the arc, are completely en¬ 
closed in a glass globe. Figure 133 shows the ordi- 


198 


Operating and Testing 


nary method of enclosing the arc and, while there are 
many variations in detail both of the enclosing globe 
and the cap at the top, the principle of all of them is 
the same. The glass globe G either sets on an air tight 
base, or is entirely closed at the bottom The top of 
the globe is closed by a cap which is provided in the 
center with an opening through which the upper 



carbon descends. This cap is generally arranged to 
allow of some play sideways so that the carbon will 
not bind, should it be of slightly irregular shape, and 
the joints between the cap and the globe are ground 
gmooth so as to exclude the air as much as possible. 

"When an arc is started in an enclosure of this kind 
whatever oxygen is present in the inside of the globe 
is soon consumed and the arc will then be surrounded 


















Arc Lamps 


199 


by a carbon gas. The absence of oxygen greatly les¬ 
sens the consumption of carbon, and, with one trim¬ 
ming, the lamp will bum 100 to 150 hours depending 
on the size and length of carbon used. The presence 
of this gas also allows of the use of a higher voltage 
across the arc with a corresponding reduction in the 
current strength. A steadier light is also obtained. 

Another peculiarity of the enclosed arc will be no¬ 
ticed in Figure 133, where it will be seen that the 
carbons do not burn to points but remain somewhat 



Figure 134 


flattened. This results in a better distribution of the 
light. The enclosed arc requires a voltage of from 72 
to 80 volts at the arc, the carbons being separated 
about % of an inch, and is, therefore, much better 
suited for operation in multiple on 110 volt circuits. 
The arc being completely enclosed, makes the lamp 
safe for operation in most any location. 

The general principles upon which arc lamps are 
constructed will be explained in connection with the 
following figures: 































200 


Operating and Testing 


Figure 134 shows in simplified form the circuits of 
the ordinal differential arc lamp. The series coil 
M (shown by the heavy lines), is connected directly 
in series with the carbons, while the shunt coil A 
(shown by the light lines) is connected in shunt 
around the arc. These coils are so wound and con¬ 
nected that, when energized, they attract the core S 
in opposite directions, the series coil M tending to 
draw it down and the shunt coil A up. The move¬ 
ment Of the core depends upon the difference between 
the attraction of the two coils, therefore it is known 
as the “differential” winding. Any movement of 
the core S is communicated by means of the lever arm 
to the upper carbon. 

Normally, in this form of lamp, the carbons are in 
contact when the lamp is not burning. The operation 
of the lamp is as follows: Current entering at the 
positive binding post P has two paths by means of 
which it may get to the negative binding post N. One 
of these paths is through the high resistance winding 
A, and the other through the low resistance offered 
by the series coil M and the two carbons which are in 
contact. It is evident that the current will take the 
easier path through the coil M and this coil will then 
become energized and the core S will be drawn down¬ 
ward, the upper carbon at the same time being raised, 
separating the carbon points and producing the arc. 
As soon as the arc is formed more or less resistance, in¬ 
creasing with the length of the arc, is introduced into 
the circuit of the series coil and some current will 
now flow through the shunt coil A, energizing this 
coil and attracting the core S in an upward direction. 


Arc Lamps 


201 


Obviously a point will soon be reached where the at¬ 
traction of the two coils is equalized and the upper 
carbon will come to rest. 

As the upper carbon burns away, and the length of 
the arc increases, the current through the series coil 
becomes gradually weaker and that in the shunt coil 
stronger, with the result that the core is drawn up¬ 
ward and the carbon points approach each other until 
a balance is again obtained. The mechanism through 
which the movement of the carbons is effected and 
the manner of connecting the various circuits differs 
in the several makes of lamps. Of these methods the 
following are in more common use. 

In some lamps the carbons are carried by a train 
of clock gears, and this gearing is under control of 
the two magnets, operating somewhat in the manner 
dascribed. In other forms of lamps the series magnet 
lifts the carbons direct and the office of the shunt mag¬ 
net is simply to close a short circuit around the lifting 
magnet and thus to deenergize it so that the carbons 
may feed. This operation is sometimes reversed, the 
series magnet being short-circuited after the arc has 
been produced and the movement of the carbon ef¬ 
fected by the shunt magnet. In still another style of 
lamp a small reversible motor is connected to the 
carbons in such a manner that it may either bring 
them together or separate them. The motor is pro¬ 
vided with two field windings, which oppose each 
other, and whichever is the stronger determines the 
direction in which the motor revolves. In connection 
with any of these plans it is possible to arrange so 
that the carbons may be either together or separated 





202 


Operating and Testing 


when the lamp is at rest. In the first case the first 
impulse of current separates the carbons, and in the 
other it must draw them together to start the arc. 

The diagram of the connections of a lamp designed 
to burn on a series circuit with many others is shown 
in Figure 135. This lamp has the same differential 
winding as that previously described and in additon 
is provided with an automatic cut-out, C. It will be 



noticed that the magnet winding of this cut-out is in 
circuit with the shunt coil and the current through it, 
therefore, increases as the arc grows longer. If the 
carbons fail to feed, or if the arc grows very long, 
and in consequence is extinguished, the current flow¬ 
ing through this magnet winding becomes strong 
enough to cause the armature A to be raised and the 
circuit at E is closed. The main current now passes 



























































Arc Lamps 


203 


from P, through R, to the armature A, point E, and 
to the negative terminal N. Thus the current is 
shunted around the lamp and all other lamps in the 
circuit are left burning as before. The purpose of R 
is to maintain some current in the shunt coil. This 
often starts the lamp again. This style of lamp is 
never extinguished by opening the circuit, but always 
by closing a short circuit around the lamp. 



Figure 136 


With arc lamps for use on series circuits it is essen¬ 
tial for the successful operation of the lamp that both 
a shunt and series coil be provided. For lamps to be 
used on multiple circuits, or circuits where the voltage 
is constant, and where the current flow depends only 
on the resistance, the lamp -will work successfully with 
either a shunt or series winding. Both windings are 
not necessary. 

Figure 136 shows a type of lamp which is operated 
with a series winding only. In this case the current 

























204 


Operating and Testing 


strength varies with the distance apart of the carbons. 
When the current becomes stronger the magnets be¬ 
come more powerful and draw up the upper carbon, 
increasing the separation between the carbon points. 
As the current weakens, the carbons come closer to¬ 
gether. This lamp is placed singly in circuit and is 



Figure 137 


often used on alternating current circuits. R is a 
reactance which with alternating currents takes the 
place of the resistance used with direct currents and 
prevents excessive rise of the current strength when 
the lamp is started. It is evident that a lamp of this 
tvne could not be used on a series, constant current 







































Arc Lamps 


205 


circuit, for the current flowing through the series 
coil would never alter and would not be affected by 
the separation of the carbons. While a lamp con¬ 
trolled only by a shunt coil would operate on either a 
series or a multiple circuit their use on series circuits 
is not satisfactory, for when starting the carbons must 
be separated and the shunt coils of all the lamps are 
then thrown m series, this necessitating a considerable 
voltage to start them. 

Figure 137 shows the circuits of the flaming arc 
lamp. In this lamp carbons, the cores of which con¬ 
sist of certain chemicals which give to the arc the pe¬ 
culiar color, are used. A much longer carbon is neces- 
sary with this form of lamp and the carbons are of 
small diameter. The operation of the lamp is as fol¬ 
lows : When the lamp is not burning the carbons are 
separated and no current can pass through them until 
the shunt magnet S has become energized and pulls 
over the arm A. As it does so the lever L (by means 
of mechanism not shown) draws the carbons together 
and this allows current to flow through them. A very 
strong current now passes through the series magnet 
B, drawing the arm A away from the shunt magnet S. 
This action causes the carbons to be separated and 
establishes the arc. The resistance of the arc lessens 
the current flow and consequently weakens the series 
magnet so that the shunt magnet again comes into ac¬ 
tion and partially draws the arm A away from the 
series magnet In this manner a point is soon found 
at which the arm comes to rest between the two mag¬ 
nets. As the arc burns away the shunt magnet be¬ 
comes stronger and the series magnet weaker and in 


206 


Operating and ‘Testing 


consequence the carbons are brought closer together, 
i. e., the lamp feeds. 

When the carbons have been fully consumed, the 
small chain shown at the right is drawn down to its 
limit and opens the shunt magnet circuit at C. This 
gives the series magnet full control over the arm A 
and it is drawn all the way over, thus separating the 
carbons and extinguishing the arc. 

The magnet M answers a double purpose. The se¬ 
ries winding causes a slight magnetization which tends 
to force the arc downward away from the economizer 
E. So long as current passes through the winding of 
the shunt magnet S the small spring carrying contact 
is held down and the fine wire circuit around magnet 
M is open. When, however, the shunt magnet circuit 
is opened, as by the stretching of the chain, the spring 
closes the circuit and this causes a strong magnetiza¬ 
tion to be set up in M which completely extinguishes 
the arc. This fine wire winding is used only where 
the arc is operated at high pressure and is not needed 
on 110 volt circuits. 

The operation of this lamp on alternating current 
circuits is somewhat different from that just described. 
The carbons rest in contact when the lamp is not 
burning and, instead of being controlled by the arm 
A, a small rotor which is under the influence of two 
opposing magnets is employed. When current is 
turned on the series magnet controls the rotor and 
causes it to raise the carbons and strike the arc. When 
the arc is started the shunt magnet increases in 
strength and causes the rotor to slow down. As the 
length of the arc continues to increase the shunt field 



Arc Lamps 


207 


becomes strong enough to finally reverse the rotor and 
feed the carbons together. The method of opening 
the circuit when the carbons are burned out is about 
the same as with the direct current lamp. There is 
no fine wire winding on the blow-out magnet. 

OPERATION 

The proper care and management of arc lamps re¬ 
quires first of all, that the operator be thoroughly fa¬ 
miliar with the principles of operation and all the de¬ 
tails of construction of the lamps under his care. It 
is well, therefore, for the operator to begin by remov¬ 
ing the jacket and carefully examine all parts of the 
lamp so as to thoroughly grasp the purpose and man¬ 
ner of operation of each part. It is also of advantage, 
if one can safely do so, to watch the operation of the 
lamp while it is burning. 

Lamps are usually trimmed in the following man¬ 
ner : Lower the lamp; remove globe; take out lower 
carbon; let down upper carbon rod and thoroughly 
clean it with crocus cloth. The successful operation 
of the lamp depends to a great extent on the condi¬ 
tion of this rod. It must be clean, so that the clutch 
will firmly grip it. It must not, by any means, be 
greasy. If the rod becomes dirty it will soon be pitted 
by the current which passes to it from the contacts in¬ 
side the lamp and pitting once started rapidly in¬ 
creases. Remove upper carbon and place it in the 
lower holder. The length of the lower carbon should 
be measured. A handy manner of doing this is to 
prepare a gauge of proper length or file a notch in the 
pliers at the proper point. If the lower carbon is 


208 


Operating and Testing 


either too long or too short and the lamp is burned un¬ 
til the upper carbon is entirely consumed, one of the 
carbon holders will be burned. Place upper carbon 
in position and align it with the lower by turning it 
freely about to see that it centers in all positions; 
raise and lower the upper carbon several times to see 
that it works freely; clean and replace the globe and 
raise lamp to its normal position. If circuit is alive 
test lamp to see that it burns. 

It is possible for a good trimmer to take care of 100 
or more arc lamps per day, if they are close together. 
Where they are far apart and conditions are more dif¬ 
ficult, 50 lamps will be sufficient. 

If the lamp is of the enclosed type, where the lamp 
clutch feeds the carbon direct, it is necessary to ex¬ 
amine the upper carbon to see that it is straight and 
smooth. Any burs or projections should be removed 
and the carbon should be raised and lowered to see 
that it moves freely through the clutch and gas cap. 

The care of globes is also of great importance where 
enclosed arcs are used. Impurities in the carbon are 
thrown off in the form of a powder, and if this is not 
removed the useful light of the lamp will be greatly 
reduced. It is good practice to occasionally return the 
globe to the shop where they can be thoroughly 
cleaned. The gas cap must also receive careful atten¬ 
tion, for if this does not fit tightly, the operation of 
the lamp will not be satisfactory. 

The following are the principle points to be ob¬ 
served in the handling' of arc lamps: 

Be sure that the voltage is right for lamps connected 




Arc Lamps 


209 


in multiple and the current for lamps connected in 
series. 

Never switch a multiple lamp by shunting the cur¬ 
rent around it; always open the circuit. 

Never open the circuit of a series lamp; always 
shunt the current around them. 

Never try to burn a multiple lamp without an 
additional resistance in the circuit. 

Never place a resistance in the circuit of a series 
lamp. 

Never handle high tension lamps without insulating 
yourself from the ground. 

It is inadvisable to touch the wires on opposite sides 
of the lamp at the same time. To be safe in this respect 
confine yourself to working with one hand at a time. 

Keep all parts of the lamp clean, especially the rod 
and the globe. 

Provide spark arresters for all open arc lamps 
where there is inflammable material. 

Never leave a lamp without globes where the wind 
can strike it. The arc will be continually blown out 
and consume carbons very fast. 

If an arc casts shadows or throws considerable light 
upward, it is an indication that it is burning upside 
down. To make sure that the lamp is burning upside 
down, separate the carbons; the one that is red far¬ 
ther from the point is the positive. 

A green light coming from the lamp indicates that 
the carbon holders are being consumed. This will 
generally occur if the lamp is left burning upside 
down for a considerable length of time, or if the car¬ 
bons are not of the nroner length. 




210 


Operating and Testing 


TESTING 

For the testing of an arc lamp practically all that 
is needed is a reliable voltmeter and ammeter. If se¬ 
ries lamps are being tested, it is essential that the ma¬ 
chine furnishing current to the testing circuit be in 
good condition and regulated properly. If a multi¬ 
ple lamp is being tested the voltage of the supply cir¬ 
cuit should be constant. The lamp should be located 
away from draughts of air and with series arcs special 
precautions must be taken to see that the place upon 
which the operator stands is well insulated and that 
under no circumstances can contact be made with the 
lamp and a ground at the same time. This is of great 
importance where tests are made on a regular circuit 
which is in use. 

Current and voltage tests can be made and the lamp 
accurately adjusted to the current and voltage for 
which it is designed. Detailed instructions are gener¬ 
ally given by the manufacturers for the adjustment 
of each particular type of lamp. These adjustments 
are generally obtained by altering the connections on 
the variable resistance or by changing the tension on 
the springs. Voltage readings should be taken as the 
lamp feeds and the cut-out if a series lamp, should 
also be tested to see that the lamp cuts out at the 
proper voltage. This test is made by slowly separat¬ 
ing the carbons until the arc breaks. One of the most 
common causes of trouble will be found in the cut-out 
and this should be thoroughly cleaned and tested. A 
defective cut-out generally results in burned out coils. 


Arc Lamps 


211 


SERIES ARC SWITCHBOARDS 

The switching of series arc light circuits is a prob¬ 
lem altogether different from any other. At the pres¬ 
ent time, very few new systems of this kind are in¬ 
stalled, but there are still quite a number of old in¬ 
stallations that must be reckoned with. 

Figure 138 shows diagrammatically the well known 
Thomson-Houston switchboard. In this system there 

\ f / \t/ 



are two horizontal rows of holes, one at the right and 
one at the left for each machine. There are also two 
vertical bars containing holes for each circuit on the 
board. The board may be built for any number of 
circuits or machines. The lower row of holes is extra 
and is provided to facilitate connecting several or all 
of the machines or circuits in series. 

The machines are connected to the circuits by means 





























































212 


Operating and Testing 


of plugs which pass through from the front of the 
board and connect the horizontal bars to the vertical 
at whatever point a plug may be inserted. If a plug 
be inserted where the positive side of machine A con¬ 
nects to circuit 1 and another where circuit 1 feeds 
into the negative side of the same circuit, machine A 
will be in position to operate this circuit. The position 
of plugs is indicated by the black circles and by trac¬ 
ing out the circuits it will be seen that machine B is 
supplying circuits 2 and 3. All of the positive leads 
of the machines go to one side of the board and the 
positives of the circuit must be connected to the same 
side. Whenever it is desired to run several circuits 
from one machine the negative of the first circuit must 
be connected to the positive of the next. 

If circuit 3 is to be disconnected from machine B, 
insert plug where circuit 2 crosses bar of machine B, 
at the right of board. This will put out the light of 
3 and the plugs may now be withdrawn. 

Another style of switchboard for the same purpose 
is shown in Figure 139. Here the connections from 
machine to circuit and from circuit to circuit are 
made by flexible cables, which carry suitable plugs at 
each end. In this diagram machine A is supplying 
circuit 1 and machine B circuits 3 and 4. Three holes 
are provided at the terminals of each circuit and 
machine to allow of the use of auxiliary plugs in 
switching. If circuit 2 is to be added to machine A, 
auxiliary plugs are used as shown by dotted lines. 
The main cable C from minus side of circuit 1 may 
now T be withdrawn. This will force current through 
circuit 2 and the permanent plugs may now be placed 


Arc Lamps 


213 


in the center of the holes. If circuit 2 should contain 
many lights or be open, a long flash would accompany 
the withdrawal of the plug. 

To disconnect circuit 3 from machine B insert aux¬ 
iliary plug, as indicated by broken line and withdraw 
cables D and E. 

When it is desired to dispense with one of the ma¬ 
chines and let the other do all of the work, the trans¬ 
fer can be made without disturbing the lights by first 



connecting the two machines in series on all of the 
circuits in use. When this is done, short circuit the 
fields of the machine A that is to be cut out, and then 
short circuit the whole machine and disconnect it. 

Switching arc circuits is somewhat confusing to one • 
who is not familiar with it, and it is advisable for any 
beginner to study out the best methods for the par¬ 
ticular board with which he has to work. He should 




















































































214 


Operating and Testing 


have the whole system in his head so as to avoid th° 
necessity of studying over the problem when circuits 
are to be changed in a hurry. 



Figures 140 and 141 show methods of controlling 
alternating current arcs operating in series. In Fig- 



_> /_v/_\✓ 

✓\ ✓ */\ 

Figure 141 

ure 140 the weight W balances the two cores of the 
coils M. When a current passes through these coils 
they draw in the cores and in so doing increase the 







































































Arc Lamps 


215 


reactance of the circuit. This in turn cuts down the 
current. In the above manner the device automatic¬ 
ally regulates the current and keeps it very close to 
its predetermined value. This device is used only for 
constant current arc lamps. 

A somewhat different principle is employed in Fig¬ 
ure 141. In this figure P is the primary coil of a 
series transformer and the current from the gen- 






Figure 142 


erator always passes through it. This current induces 
secondary currents in the coil S. This coil is balanced 
by the weights W, and is free to move up or down. 
If the current in the secondary increases beyond a 
predetermined amount, the repulsion between the two 
©oils is increased and the upper one rises. This les¬ 
sens the induction and cuts down the current. If the 
current becomes weak, the operation is reversed. 






















216 


Operating and Testing 


Where it is desired to use direct current arc lamps 
from alternating current circuits, the Cooper-IIewitt 
Mercury Rectifier is often used. A diagram of the 
connections of this device is shown in Figure 142. The 
principle upon which this is based is outlined in an¬ 
other chapter and need not be repeated here. It is 
well known that the current can pass from the posi¬ 
tive electrodes P into the negative or mercury elec¬ 
trodes N when once established, but cannot pass from 
the negative electrode to the positive. 

In order to start the operation, the glass bulb is 
tilted a little so that the mercury of the two lower 
electrodes unites; this starts current from the starting 
transformer S and when the bulb is returned to its 
normal position the current breaks, causing an arc. 
This allows current from whichever of the upper elec¬ 
trodes is positive at the time, to pass into the negative 
and feed the arc lamps. As the polarity of the upper 
electrodes unites; this starts current from the starting 
negative ceases and that from the one that is now 
positive begins. 

A reactance which will cause the current from the 
first pole to overlap that of the succeeding one must 
be provided, or the current will cease entirely should 
it ever go to zero. 


CHAPTER XVI 


INCANDESCENT LAMPS 

For the illumination of small spaces such as offices, 
residences, etc., the incandescent lamp is without doubt 
the most useful and economical. This is principally 
due to the even distribution of light which the small 
units make possible, and to the readiness with which 
the lamps may be adapted to numerous lighting 
schemes. 

Originally all commercial incandescent lamps were 
made with carbon filaments, but within the last few 
years new types of filaments have been developed and 
these are, to a great extent, replacing the carbon fila¬ 
ment. 

In the carbon filament lamp a filament or thread is 
formed of some material rich in carbon, fibers of 
bamboo being originally used for this purpose. At 
the present time practically all carbon filaments are 
made by forcing a cellulose compound through suita¬ 
ble dies, the filament being hardened, cut to the proper 
length and placed on forms. It is then entirely sur¬ 
rounded by carbon in some form, so as to exclude all 
air and heated for several hours in a furnace. 

After it is cooled the filament is removed from the 
form and connected to the leading in wires. The 


217 


218 


Operating and Testing 


substance of which the leading in wires is composed 
must expand and contract at the same rate as the 
glass surrounding it, otherwise the glass would be 
broken or a space would be left where the air could 
enter the lamp. This substance must also be of such 
a nature as to withstand the high temperature at 
which the glass is fused and the heat of the filament. 
Platinum is about the only material that fulfills these 
conditions and is used for this purpose. 

The filament is now subjected to what is known as 
the “flashing” process, being placed in a chamber 
filled with a hydrocarbon vapor and current passed 
through the filament until it is heated to a low de¬ 
gree of incandescence. Any irregular portions of 
the filament will be heated to a higher temperature 
and carbon will be deposited to a greater extent at 
these points. When all parts are uniform and the 
filament is of the proper resistance, the process is 
stopped. In good lamps heated to a dull red, the fila¬ 
ment should appear uniform throughout. If there 
are bright spots the filament will quickly burn out at 
one of these places. 

After flashing the filament appears gray in color, 
with a hard outer surface which increases the useful 
life of the lamp and adds to its efficiency. 

The filament is now placed in the glass globe and 
the air is then exhausetd by mechanical or chemical 
means. A good vacuum is of great importance. The 
presence of oxygen hastens the deterioration of the 
filament. The presence of any gas inside the lamp 
increases the loss of heat in the filament and there¬ 
fore reduces its efficiency. This also increases the de- 


Incandescent Lamps 


219 


terioration of the filament through friction between 
the filament and the gas. In a poor vacuum vibration 
of the filament will cease quickly. 

Incandescent lamps are rated according to theii 
candlepower, the sixteen-candlepower lamp being the 
size most generally used. The lamp is also made in 
various sizes from 2 to 50-candlepower. 

The light given out by an incandescent lamp bears 
a certain definite relation to the temperature of the 
filament, being greater as the temperature of the fila¬ 
ment is increased. The current taken by the lamp 
depends upon the resistance offered by the hot carbon 
filament. It can readily be seen that we might have 
two incandescent lamps, each giving out a light equiv¬ 
alent to 16-candlepower, but one taking considerable 
more current than the other, as, for instance where 
one lamp has a short filament of small cross section 
ind the other a long filament of larger section. It is 
evident that to intelligently compare lamps, the rela¬ 
tion between the amount of energy consumed and the 
amount of light given out by the lamp must be 
known. This is termed the “efficiency” of the lamp, 
and is obtained by dividing the total watts consumed 
by the lamp by the candlepower. 

Total Watts 

Candlepower 

If a lamp consumes 56 watts and gives a candle- 
power of 16, the efficiency is 56 -f- 16 = 3.5 watts per 
candle. 

It may be noted that the term “efficiency” is some¬ 
what of a misnomer as here used. A 16-candlepower 



220 Operating and Testing 

lamp consuming 50 watts, has an efficiency of 3.1, the 
efficiency in this case as expressed numerically being 
less than in the case previously stated, while, as a 
matter of fact, the real efficiency of the lamp is higher 
as it consumes fewer watts per candle. Nevertheless, 
the term has come into general use and when ex¬ 
pressed in a certain number of watts per candle con¬ 
veys the actual comparative rating of the lamp. Low 
candlepower lamps are generally less efficient than 
the standard sizes and the 220-volt lamps are less ef¬ 
ficient than those of 110. Table I shows the wattage 
and current for lamps in general use. 

The efficiency in lamps of the same type of filament 
depends upon the temperature of the filament. The 
higher the temperature the brighter the filament and 
the less the number of watts per candle. A tempera¬ 
ture of about 2500° F., is maintained in the carbon 
filament. After a lamp has been in use for some time 
the filament gradually disintegrates, the carbon which 
is thrown off by the filament depositing on the inside 
of the glass globe. The light emitted from the lamp is 
thereby greatly reduced and the watts per candle in¬ 
creased. The disintegration of the filament is more 
rapid the higher the temperature. 


Incandescent Lamps 


221 


TABLE I. 


RATING OF INCANDESCENT LAMPS. 


Carbon Lamps, 110 Volts. 

C. P. 

Watts 

Amperes 

2 

13 

.11 

4 

18 

.16 

6 

24 

09 

8 

30 

.27 

10 

35 

.32 

12 

40 

.36 

10 

56 

.51 

20 

70 

.64 

24 

84 

. 76 

32 

112 

1.00 

00 

175 

1.60 

Carbon Lamps, 220 Volts. 

C. P. 

Watts 

Amperes 

8 

36 

.16 

10 

45 

.20 

1G 

64 

.29 

20 

76 

. 35 

24 

90 

.41 

32 

122 

.55 

50 

190 

. 86 

Gem Lamps, 110 Volts. 

C. I*. 

Watts 

Amperes 

20 

50 

.45 

40 

100 

.91 

50 

125 

1.14 

75 

187 

1.70 

100 

250 

2.27 

Tantalum Lamps, 110 Volts. 

C. P. 

i Watts 

Amperes 

20 

40 

.36 

40 

80 

.73 

Tungsten Lamps, 110 Volts. 

C. P. 

Watts 

Amperes 

32 

40 

.36 

48 

60 

. 55 


It is evident from the foregoing that there are two 
main factors effecting the usefulness of an incandes¬ 
cent lamp. By increasing the efficiency we shorten 
the life and by decreasing the efficiency we increase 
the life of the lamp A lamp taking 3.5 watts per 
candle has a useful life of about 800 hours. By burn¬ 
ing the lamp at 4 watts per candle the life of the lamp 
would be extended to about 1,800 hours. 













































222 


Operating and Testing 


The cost of current will generally determine the 
proper lamp to use. When the cost of current is low, 
a low r efficiency lamp may be used, and when the cost 
of current is high, a high efficiency lamp should be 
used. A point to be considered in the use of high 
efficiency lamps is the pressure or voltage at which the 
lamp is burned. For economical and satisfactory op¬ 
eration, the pressure must be maintained practically 



Figure 143 


uniform. With the filament already at a high tem¬ 
perature even a slight increase in voltage will produce 
a considerable increase in the temperature of the fila¬ 
ment and a corresponding decrease in the life. This 
is not of so much importance where low efficiency 
lamps are used as a slight increase in the voltage does 
not produce such an excessive rise 4n the temperature 
of the filament. 










































































































































Incandescent Lamps 


223 


The manner in which the candlepower, watts per 
candle, and the life of 3.5 watt carbon lamps vary 
where burned at voltages greater or less than their 
normal voltage is shown in Table II, which table is 
given by the estinghouse Co. and represents the 
average of a number of tests. The values given in 
the table are plotted on the curves in Figure 143. It 
will be noted that an increase of 3 per cent in the 
voltage reduces the life of the lamp to one-half, while 
an increase of 6 per cent decreases the life to one-third. 


TABLE II. 

INCANDESCENT CARBON LAMPS. 

Effect of Variation of Voltage on Candle Tower, Efficiency and Life. 


Volts 


Per cent. 
110 
109 
108 
107 
106 
105 
104 
103 
102 
101 
100 
99 
98 
97 
96 
95 
94 
93 
92 
91 
90 


Candle 

Power 


Per cent. 
169 
161 
153 
145 
138 
131 
124 
118 
111 
106 
100 
95 
90 
85 
80 
75 
71 
67 
63 
59 
55 


Watts per 
Candle 

Per cent. 

72 

74 

76.5 
79 

81.5 
84 
87 
90 
93 

96.5 
100 
103 
106 

109.5 

113.5 

118.5 

123.5 
128 
134 

140.5 

147.5 


Life 


Per cent. 
15 
18 
21 

24.5 

29 

34 

40 

48 

60 

80 

100 

120 

147 

175 

200 

270 

355 

450 

545 

650 

760 


As an illustration of the use of the table assume 
the case of a 16-C. P., 110-volt lamp consuming 3.5 
watts per candle and having a life of 800 hours. If a 
lamp of this rating was burned on a circuit where the 




















224 


Operating and Testing 


voltage was 120, or 109 per cent of its normal voltage, 
the candlepower would be increased to 161 per cent 
of the normal or 25.8 C. P.; the watts per candle 
would be reduced to 74 per cent, or about 2.59; the 
life would be decreased to 18 per cent, or 144 hours. 

If a 16-C. P., 3.5 watt lamp, designed for use on an 
115-volt circuit, was burned on a circuit at 110 volts 
or 95.5 per cent of the normal, the candlepower would 
be decreased to 77.5 per cent or 12.4; the watts per 
candle to 116 per cent, or about 4; the life increased 
to 237 per cent, or about 1,880 hours. 

It is an inexcusable, though very natural, mistake 
to suppose that there is any economy in burning lamps 
after their candlepower has been greatly reduced. As 
a rule, if a lamp be burned about 1,000 or 1,200 hours 
the candlepower will have fallen to one-half of its 
initial value, while the current consumption will re¬ 
main about the same. Consider the following exam¬ 
ple : A 50-watt lamp burning 600 hours will consume 
30,000 watts, which at ten cents per kilowatt will cost 
$3.00. The cost of the lamp will not be more than 20 
cents. If now the lamp be burned for 600 hours 
more, it will give out about 8 candlepower and the 
cost of the current consumed will be another $3.00, 
whereas the cost of a new lamp of 8 candlepower, 
which would give its equivalent in light, would cut 
the cost of current down to one-half or $1.50 and the 
cost of the new lamp would be only 20 cents. It will 
be seen that the user, who is trying to save something 
by getting along with a dim light, is losing half his 
light to save 20 cents, and at the same time paying out 
$1.30 more than would be required to obtain the same 







Incandescent Lamps 


:1>5 

illumirmtion with a new lamp of the same candlepower 
as the old one is actually giving him. 

The useful life of a lamp is determined by the num¬ 
ber of hours the lamp will burn before the candle- 
power has dropped to 80 per cent of its original value. 
This is known as the “smashing point,” and it is sel¬ 
dom economical to burn the lamp after this point has 
been reached. 

When lamps become old and dim, the candlepower 
can be increased by increasing the voltage, but this is 
poor practice for, of necessity, the voltage on what¬ 
ever new lamps may be in circuit is also increased and 
this does more harm in shortening the life of these 
lamps than good in saving the old. 

The efficiency and the life of incandescent lamps 
are two factors which do not harmonize. The higher 
the efficiency of a carbon filament lamp the shorter 
its life. This makes it advisable to carefully consider 
which is the most economical lamp to use. The two 
main considerations in determining the most econom¬ 
ical lamp are the cost of current and the cost of lamp 
renewals. Tables III and IV are prepared to facili¬ 
tate calculation in this regard. The most economical 
lamp to use is that in which the cost of energy and 
the cost of renewals is a minimum. If the cost of 
power is high, a lamp of high efficiency, even though 
its life be short, is generally more economical; while 
if power is very cheap, a lamp of low efficiency is gen¬ 
erally advisable. 

TABLES 

In Table III, the cost of current per kilowatt is 
given at the top of the columns, and the watts per 


226 


Operating and Testing 


candlepower of the lamp in the left-hand vertical col¬ 
umn. Wherever two columns cross will be found the 
cost per candlepower for 1,000 hours for the lamp of 
an efficiency as indicated in the left-hand column, and 
at the cost per kilowatt as shown at the top of the 
column. As an example: Take a lamp of an effi¬ 
ciency of 3.1 watts per candle, with current costing 
10 cents per kilowatt. Where these two columns in¬ 
tersect in the table will be found the value, .310; show¬ 
ing that the cost per candlepower per 1,000 hours at 
this efficiency and rate will be 31 cents. 

To ascertain the cost of current consumed by a 
lamp of any candlepower per 1,000 hours, the cost as 
found in the table must be multiplied by the candle- 
power of the lamp. For instance: a 16-candlepower 
lamp at the rating shown above, would cost 16 X -31 
m $1.96 for 1,000 hours burning. 

Table IV deals with the cost of lamp renewals. In 
the upper horizontal row is given the life of the lamp 
in hours, and at the left hand vertical column the 
cost of the lamp in cents per candlepower. Wherever 
the two columns cross will be found the cost of lamp 
renewals per 1,000 hours. 

Example: Suppose a 16-candlepower lamp costs 19 
cents (1.2 cents per candle) and has a life of 600 
hours. In the row at the right of 1.2, and in the col¬ 
umn headed 600 will be found the value, .02, which 
is the cost of the lamp renewals per candlepower for 
1,000 hours. For a 16-candlepower lamp, the cost 
would be 16 X .02 = $0.32. The total cost of the 
lamp for 1,000 hours, including both cost of current, 
and renewals, is $4.96 -f- $0.32 = $5.28. 


Inca ndescc ac Lamps 


* 


227 


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228 


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To find tlie most economical lamp where the cost of 
current is fixed, it is only necessary to try out several 
cases and select the one where the sum of the two fac- 















































Incandescent Lamps 


229 


tors is a minimum. In comparing lamps of either the' 
same or different candlepowers, it is not necessary to 
multiply the values found in the tables by the candle- 
power of the lamp. On the other hand, where the 
actual cost per 1,000 hours is desired, the values 
found in the tables must be multiplied by the candle' 
power of the lamp in question. 

As an example showing the method in which the 
table is used the two following lamps will be com¬ 
pared : 

Sixteen-candlepower carbon lamp of an efficiency 
of 3.5 watts per candle, life of the lamp 1,150 hours, 
cost of the lamp 16 cents (1 cent per candle). 

Thirty-two-candlepower Tungsten lamp of an effi¬ 
ciency of 1.25 watts per candle, life of lamp 1,000 
hours, cost $1.20 (3.7 cents per candle). 

Cost of current, 10 cents per kilowatt. 


For the carbon lamp: 

Table III gives.35 

Table IV gives.009 


Total.359 

For the Tungsten lamp: 

Table III gives. 125 

Table IV gives. 035 

Total.160 


The result shows that for the values taken the cost 
of the Tungsten lamp will be less than one-lialf that 
of the carbon lamp. 









230 


Operating and Testing 




It will be noted that in using the tables, the cost 
per candlepower of the Tungsten lamp is 3.7 cents is 
not given in the table, and the value 3.5 is taken. If 
greater accuracy is desired, the values may be inter¬ 
polated. For instance: in the case given, the value 
from Table IV would be .037, giving a total of .162 
in place of .160. 

Arc lamps, Nerast lamps, or, in fact, any lamps 
where the candlepower, efficiency and cost are known 
may be compared; either two lamps of the same type, 
or lamps of different types. 


METALLIZED FILAMENT LAMP 


In the past few years a number of new types of 
incandescent lamps have been developed. The qual¬ 
ity of the light, the life of the lamp, its regulation 
and its efficiency have all been greatly improved. The 
first of these lamps to come into general use is known 
as the metallized filament lamp. The filament of this 
lamp is of carbon, which is put through various proc¬ 
esses, one of which is the heating of the filament to a 
very high degree in an electric furnace. Practically 
all the impurities are driven out by this process and 
a greatly increased efficiency is obtained, and the fila¬ 
ment gives out a much better quality of light. 

One of the peculiar results effected by the treat¬ 
ment of the filament, and the one from which it gets 
its name, is that the electrical characteristics of the car¬ 
bon is considerably changed. The ordinary carbon 
filament has a negative temperature coefficient; in 
oP'er words, its resistance lowers with an increase in 









Incandescent Lamps 


231 


temperature and increases with a lowering tempera¬ 
ture. On a system where the voltage regulation is 
poor, the effect of the negative temperature coefficient 
is, so far as the light is concerned, cumulative, the in¬ 
crease in voltage causing, in itself, more current to 
flow through the lamp, increasing its candlepower. 
The increase in current increases the temperature of 
the filament and lowers its resistance, this causing a 
still further increase in the candlepower. 

The metallized filament has a positive temperature 
coefficient, similar to metals. Its resistance increases 
as its temperature increases. The regulation of the 
lamp is therefore much better than that of the carbon 
lamp, an increase in voltage causing an increase in 
the resistance of the filament and a corresponding ten¬ 
dency to check the current rise. This lamp has 
an efficiency of 2.5 watts per candle, or 40 watts for 
a 16-candlepower lamp. 

TANTALUM LAMP 

The Tantalum lamp is another recent development 
in the field of incandescent lighting. This lamp takes 
its name from the metal from which the filament is 
constructed. Tantalum is one of the rare metals and 
not only has a greater strength than steel, but is capa¬ 
ble of withstanding a very high temperature. Due to 
these characteristics the metal is very well suited for 
use as a filament. 

As all metals are of comparatively low resistance 
a filament of unusual length must be employed to ob¬ 
tain the proper resistance. The Tantalum lamp has 


232 


Operating and Testing 


.an efficiency of 2 watts per candle and gives a very 
white light resembling daylight. It is not recom¬ 
mended for use on alternating current circuits. 

TUNGSTEN LAMPS 

Shortly after the introduction of the tantalum lamp 
a still greater advance was made by the bringing out 
of the Tungsten lamp. Tungsten, another of the rare 
metals, is in its electrical behavior similar to tantalum 
but for use as a filament it surpasses tantalum, owing 
to the fact that its melting point is considerably 
higher. The filament can be burned at a very high 
temperature and has an efficiency of 1.25 watts per 
candle. The filament being of metal has a compara¬ 
tively low resistance and, as with tantalum, must be 
unusually long to obtain the proper resistance for use 
on the common voltages. 

The current required for producing equal candle- 
power with Tungsten lamps is approximately one- 
third of that required by carbon lamps, and approxi¬ 
mately one-half of that required by the metallized 
filament lamps. The cost of operating Tungsten lamps 
is, therefore, much less than the cost of operating 
other lamps. 

The light given by the Tungsten lamp is much 
whiter and more pleasing in character than that given 
by other lamps. As its quality corresponds more 
nearly to sunlight than any other artificial illuminant 
it is especially desirable for use in show rooms, stores, 
etc. The loss in candlepower after the lamp is in use 
for some time amounts to about one-fourth that of the 


Incandescent Lamps 


233 


carbon lamp. The lamp also has a much longer life 
than the carbon lamp. In regulation the Tungsten 
lamp is greatly superior to the carbon lamp and an 
excessive voltage which would ruin a carbon lamp 
does not seriously affect the Tungsten lamp. 

Tungsten being quite brittle and the filament of 
necessity being of small cross section, the lamp must 
be carefully handled. The lamp should be cleaned 
while hot, as the filament is then stronger than when 
cold. It is also advisable to control the lamp from 
switches, thus avoiding the jarring caused by turning 
on at the socket. It has been customary to burn the 
lamp with the filament hanging downward in a verti¬ 
cal direction this being necessitated by the sagging of 
the filament, but lamps are now made to burn with 
the lamp hanging in any direction. The filament 
after having burned for some time shrinks considera¬ 
bly and this must be provided for in the manufacture. 

With Tungsten lamps designed for use on low volt¬ 
age, the filaments are made of a much shorter length 
and are less liable to breakage. This class of lamp 
may be burned in series on the ordinary circuits of 
110 or 220 volts, or suitable transformers are no vr 
made so that on alternating current systems these low 
voltage lamps may be wired up in multiple. 

The filaments of both tantalum and tungsten can 
often be welded when broken, by shaking the lamp 
when connected in circuit, until the broken ends come 
together. As this operation generally has the effect 
of shortening the filament and lessening its resistance 
it brings with it an increase in candlepower. 


233a 


Operating and Testing 


NITROGEN-FILLED LAMPS 


The lately developed nitrogen-filled lamps have 
caused considerable comment by their extreme bril¬ 
liancy and high efficiency. The larger sizes of these 
lamps operate at a considerable advantage over all 
other incandescent illuminants 

The intrinsic brilliancy is very high and they should 
preferably be hung high enough to be out of the range 
of vision; otherwise they will be injurious to the eye. 

The temperature of the enclosing globes is very high, 
and if used out of doors where they may be struck by 
sleet or rain while hot they are likely to be broken. 

It is best to use these lamps only in special sockets 
containing no material which may be affected by the 


heat, and where wires are run close enough to be 
affected by the heat the ordinary rubber-covered, wire 


should not be used. Asbestos-covered wire is prefer¬ 
able. 

The color value of these lamps is very good and the y 
are well suited for color-matching and also for photo¬ 
graphic work, although for the latter purpose they 
are not as fast as some types of arc lamps and the 
mercury vapor lamps. 

The distribution of light from these lamps is quite 
uniform in nearly all directions and is emitted from 
a point source more nearly than that of any other 
lamp except the arc lamp. It will, therefore, throw 
strong shadows, and requires special reflectors. 

The efficiency of the smaller lamps is not much 
better than that of the ordinary mazda, or tungsten, 
lamps, but the light is more concentrated and a 












Incandescent Lamps 


233b 


greater brilliancy is obtainable. This fact makes them 
very desirable for show-window lighting. 

The following table gives approximate data concern¬ 
ing nitrogen-filled tungsten lamps: 


Volts 

105 

to 

125 


Size of lamps 
in watts 
400 
500 
750 
1000 


Efficiency in 
watts, per c. 

.75 

.70 

.60 

.55 


Amperes per 
lamp approx. 

3y 2 

4y 2 


6 

8 


£ 


234 


Operating and 'Testing 


ILLUMINATION 

Light, so far as its practical use is concerned, de¬ 
pends upon its value as a means of discrimination 
both as to form and color. The amount of light which 
is useful for this purpose is known as the illumina¬ 
tion, and depends upon the quality and strength of 
the light giving source, and its distance from the ob¬ 
ject to be illuminated. 

The unit of illumination is the candle foot, being 
the amount of light received by a surface placed at a 
distance of one foot from a light of one standard can- 
dlepower. The illumination on any surface is in¬ 



versely proportional to the square of its distance from 
the source of light. This is plainly shown in Figure 
144. If the surface A is so located that all points on 
it are at a distance of one foot from the one candle- 
power light L, the intensity of the light on this sur¬ 
face will be one candle foot. The surface B, located 
at a distance of two feet from the light L is illumi¬ 
nated over a surface four times that of surface A and 
the illumination is, therefore, decreased to one-fourth; 
or in the inverse ratio of the square of the distances 
from the source of light. 

A 16-candlepower lamp would produce an illumi- 











Incandescent Lamps 


235 


nation of one candle foot on a surface located four 
feet away from the lamp, and this is considered suf¬ 
ficient for all ordinary purposes, but for brilliant il¬ 
lumination much greater intensities are often used. 
Table V gives,‘for different classes of lighting, the 
amount of illumination in candle feet and the corre¬ 
sponding area in square feet for each 16-candlepower 
lamp, to produce this illumination. 

table v. 


Square feet per 
lamp, lamps four 
feet above object. 

Halls .1 to 3 candle feet 60 to 20 

Reading .1 to 3 candle feet 60 to 20 

Desk . -...2 to 4 candle feet 30 to 15 

Book keeping.2 to 4 candle feet 30 to 15 

Clothing stores.4 to 6 candle feet 15 to 10 

Drafting, engraving.5 to 10 candle feet 12 to 6 


In using this table the color of the walls must be 
taken into consideration. With dark walls, the great¬ 
est number of candle feet should be used. 



With an incandescent lamp the light is not given 
out uniformly in all directions. The distribution of 





























236 


Operating and Testing 


light from a 20-candlepower metallized filament 
lamp is shown in Figure 145, where the candle- 
power taken at various angles in a vertical plane 
are plotted. The concentric circles represent the can- 
dlepower marked on them 

The curve of light distribution varies in the several 
types of lamps, and is greatly affected by the shape of 
the filament. It will be seen from the curve, Figure 
145, that a considerable amount of light is given out 

90* 

75* 

60* 


45* 


30* 15* 0’ 15* 30‘ 

Figure 146 

0 

in a horizontal direction while, as a general rule, the 
greatest light is desired below the lamp. By the use 
of suitable reflectors almost any distribution of the 
light desired may be obtained and the effect, so far 
as the candlepower at points below the lamp is con¬ 
cerned, is clearly shown by the curve, Figure 146. 
Here the maximum light is given off at an angle of 
40° and the lamp is much more useful for ordinary 
purposes. 















Incandescent Lamps 


237 


The amount of illumination at any given point over 
an area will depend upon the candlepower of the 
lamp, the distance from the lamp and the angle that 
the surface makes with the line of the direction of the 
light. The first two factors have been explained and 
the last one will be readily understood from every day 
experience, it being well known that the greatest 
amount of illumination, in reading, for instance, is 
obtained when the paper or book is so held that the 
light strikes it at right angles. The curve, Figure 147, 
represents the illumination at various points at differ¬ 
ent distances from the source of light. If two similar 
lamps are placed 16 feet apart, the resultant illumina- 



Figure 147 

tion will be equal to the sum of the two curves A and 
B or as shown by curve C. 

To lay out a curve of this kind it is necessary to 
know first the curve of the distribution of the particu¬ 
lar lamp used. It is also necessary to know the pro¬ 
portion of light reflected at right angles to the surface, 
where the light strikes the surface at an angle. 

That the color of the walls and ceiling of a room 
has a great effect on the amount of useful light is 
shown from Table VI, which gives the coefficient of 
reflection for various colors. As the light reflected 
from the walls and ceilings is but a small proportion 






































238 


Operating and Testing 


of the total light, the values shown are only useful in 
comparing the several wall colors. The size of the 
room and the use of reflectors will also greatly modify 
the effect of the wall coloring. 

TABLE VI 

Coefficient of 

Color of Wall. Reflection 

White paper.70 

Chrome yellow. 62 

Orange paper.50 

Plain deal (clean).45 

• 

Yellow paper.40 

Yellow painted wall (clean).40 

Light pink paper.36 

Plain deal (dirty).20 

Yellow painted wall (dirty).20 

Emerald Green Paper.18 

Dark brown paper.13 

Vermilion paper.12 

Blue green paper.12 

Cobalt blue paper.12 

Deep chocolate paper.04 

Good illumination requires that the light be of suf- 
ficient strength to plainly discern the object illumi¬ 
nated. The light must be uniform. A flickering or 
streaky light is very bad on the eyes. The light should 
not be exceedingly strong, as a strong light is very 
injurious to the eye; nor should the light be too dim, 
as the eve strain is considerablv increased. The lights 
should always be so arranged that the direct rays of 
light do not fall on the eve. 




















CHAPTER XVII 

NERNST LAMP 

Figure 148 shows a diagram of the Nernst Lamp. 
The glower G (which emits the light) is composed of 
an oxide which when cold is of quite high resistance, 
but this resistance is lowered as the temperature rises. 
When the switch is closed the current passes 



Figure 148 


through the fine wire of the heater H which soon heats 
the glower so that current begins to flow through it. 
When this current attains approximately its normal 
value the magnet M attracts the cut-out C and in so 
doing opens the heater circuit and prevents further 
consumption of energy. B is a fine iron wire resist¬ 
ance which serves to steady the current. The resist- 


239 























240 


Operating and Testing 


ance of the iron wire increases as the current increases 
and thus exerts a steadying effect. 

This lamp gives out a very serviceable white light 
and is of much higher efficiency than the ordinary 
carbon filament incandescent lamp. A glower that 
consumes about 88 watts is supposed to yield about 
60 candlepower. 

The starting current is always about 20 per cent 
in excess of the normal operating current. 

These lamps can be had in a great variety of sizes, 
either for 110 or 220 volts, and for either direct or 
alternating current. On alternating currents the life 
of the lamp is, however, much longer than on direct 
current circuits. 

As the glowers are always located at the bottom of 
the frame the distribution of the light is very good 
and reflectors are not needed. 

COOPER-HEWITT LAMP 

Figure 149 shows a diagram of the connections of 
the Cooper-Hewitt Lamp for direct currents. These 
lamps each contain a small quantity of mercury 
through which the current must be established for a 
short time and then broken. This is accomplished by 
tilting the tube slowly so that the mercury in it run¬ 
ning from the high to the low side forms a continuous 
stream and allows the current to start. After the cur¬ 
rent is started the mercury continues to run to the 
low end and finally breaks the circuit; but the current 
now continues to flow and produces a greenish light 
of very high actinic quality. The lamp is extremely 
well suited for photographic purposes. Great care 



Cooper-Hewitt Lamp 


241 


must be exercised that the lamp is connected properly 
with reference to polarities. Current passing through 
it in the wrong direction will quickly ruin the lamp. 
The circuit can readily be traced in the figure. When 
the main switch is closed and before the lamps are 
tilted the current passes through the resistances R and 
the contacts M. W hen one of the lamps is tilted and 
current established through it the magnet is energized 
and attracts the armature M, thus cutting out the 



Figure 149 


path through the small resistance in parallel with the 
lamp. Should one lamp fail to \^ork, the current 
through the magnet would cease and the armature fall 
thus closing the circuit so that the other lamps may 
remain in use. The main switch should never be left 
closed while the lamps are not in use as current would 
be continuously flowing. 

The lamps must not be used with the negative elec¬ 
trode tilted too high up. 



























242 


Operating and Testing 




The current should never be allowed to exceed 4 am¬ 
peres and should normally not exceed 3%. The re¬ 
sistances R are adjustable and should be set for thif 
current value. 

These lamps are sometimes arranged to be started by 
a high induced E.M.F., an induction coil is arranged 
to send a momentary kick of current through the tube 
which starts the lamp. Sometimes, also, two lamps are 
mounted on one frame and started together. In suck 
a case the shunt circuit around the lamps may be 
omitted. The life of the tubes is said to be about 
1600 hours. 







CHAPTER XVIII 


INSTRUMENTS FOR TESTING 

Probably the easiest and simplest way of testing is 
by “ tasting/ ’ This is done by placing the two ends 
of the wire being tested on the tongue. The passage 
of current from one wire to the other over the tongue 
decomposes the saliva on the tongue and leaves a salty 
taste. This salty taste is an indication of current 
flowing. If there are several cells of battery connected 
to the line one wire may be held in the hand and the 
other placed on the tongue or, if one terminal of the 
batteries is grounded, a person standing on wet or 
moist ground can taste the current by placing one wire 
on the tongue. 

Obviously this test is very limited, being used as a 
rule only in bell work to ascertain if current is ob¬ 
tainable at a certain point. Some care must be exer¬ 
cised, in using a test of this kind, not to allow the 
wires to come together on the tongue, as a considerable 
spark is obtained when a circuit containing magnets 
is broken. 

Another test in which the chemical effect of the cur¬ 
rent may be used to determine both the presence of, 
and the direction of, flow of current consists in holding 
the two ends of wire being tested in a cup of water or 


243 


244 


Operating and Testing 


a solution of water and salt or water and acid. The 
presence of the current will be indicated by the for¬ 
mation of hydrogen bubbles on one of the terminals 
and ow T ing to the fact that the bubbles form on the neg¬ 
ative terminal the direction of flow of the current can 
be ascertained. 

The chemical effect of the current is also made use 
of to determine the amount of current flowing. The 
Edison chemical meter, which is now almost out of 
use, consists of two plates of zinc suspended in a solu¬ 
tion of water and acid and so connected to the main 
circuit as to allow a certain definite proportion of the 
main current to flow between the plates. The amount 
of zinc deposited on the negative plate measures the 
amount of current that has passed through the meter. 

The heating effect of the electric current is some¬ 
times made use of in testing, the mere fact of a con¬ 
ductor being hotter than the surrounding atmosphere 
generally indicating the presence of current and 
roughly the amount. 

By making use of the magnetic properties of the 
current several more convenient and satisfactory 
methods of testing are available. Probably the sim¬ 
plest of any of these methods consists of the ordinary 
vibrating electric bell, such as is used for call bells, etc., 
or a telegraph instrument. The use of a telegraph in¬ 
strument has some advantages over the bell in that it 
is more sensitive to small currents and, by varying the 
adjustment of the spring on the sounder the compara¬ 
tive strength of the current may be roughly deter¬ 
mined. 

One of the oldest testing instruments is the com- 







Instruments for Testing 


245 


pass. This in its simplest form consists of a piece of 
magnetized steel pivoted or suspended so that it can 
turn about its central point. The compass needle being 
magnetized sets up a held of force in which the lines 
of force emanate from the north pole, and encircling 
the needle enter at the south pole. As the earth itself 
is surrounded by lines of force extending from the 
north pole to the south pole, the compass needle being 
free to move tends to set itself in a north and south 
position. A wire carrying current is surrounded by a 
field of force as has been explained in previous chap¬ 
ters. When a compass is brought into the field of 
force the needle assumes a position due to the result- 



Figure 150 


ant field. By means of Ampere’s rule, which is given 
below, the direction of the current flow can be easily 
determined. 

Ampere’s rule: If a person swims with the current 
and looks at a north seeking pole it will be deflected to 
the left. The relation existing between a wire carry¬ 
ing current in a certain direction and a compass nee¬ 
dle held either above or below it is shown in Figure 
150. The direction in which the needle tends to point 
is reversed by changing it from above to below the wire 
or vice versa. 

The expansion of a wire due to the heating effect of 
the current flowing in it is made use of to indicate the 


246 Operating and Testing 

amount of current flow in the so-called 11 hot wire 
instruments. 

A wire of some length is rigidly fastened at one 
end, the other end being attached to a spring. A 
pointer is attached to the wire at the point where it 
and the spring connect On sending a current through 
the wire it becomes slightly heated and expands, the 
amount of expansion being indicated by the position 
of the pointer on a suitably graduated scale. Neces- 



Figure 151 


sarily the resistance of the instrument is quite low. 
Instruments of this kind are “dead beat” and are un¬ 
affected by external fields. They can be used on 
either direct or alternating current. 

Practically all measuring instruments in use at the 
present time operate on the principle previously de¬ 
scribed in connection with the compass needle. 

In Figure 151 is shown a tangent galvanometer. The 
wire is wound on the outside of the large ring and 
may consist of a number of turns of small wire or a 
few turns of large wire, or, as is sometimes the case, 
























Instruments for Testing 


247 


two separate windings may be used, one of fine wire 
and one of large wire. In the center of the ring is 
placed a compass needle. The length of this needle is 
small as compared with the diameter of the ring so 
that whatever position it may assume, the needle is 
always in a practically uniform field. A light pointer 
attached to the needle moves over a graduated scale. 

"When the galvanometer is used it is placed in such 
a position that the coil lies parallel with the lines of 
force of the earth’s field, i. e., points north and south. 
The current flowing in the coil is proportional to the 
tangent of the angle of deflection of the needle and it 



is from this fact that the instrument derives its name. 

The meaning of the tangent is explained by Figure 
152. The tangent of an angle is the length of the line 
from F to where a line drawn from the center of the 
circle through the angle in question intersects the line 
F G. Thus a current deflecting the needle to the point 
2 on the circle is proportional to the length of the line 
F 1 and not to the space between F 2. This type of 
galvanometer is used only in the laboratory or testing 
room. 

"Where it is desired to measure very small currents, 
as where very high resistances are to be measured, a 




248 


Operating and Testing 


galvanometer more sensitive than the tangent galva¬ 
nometer must be used. The mirror galvanometer is 
often used for this purpose. 

Figure If € shows the principle of the D’Arsonval 
galvanometer. The field of this instrument consists 
of two permanent magnets between the poles of which 
is suspended a coil of fine wire. This coil is suspended 



Figure 153 


by a wire from the screw shown at the top of the in¬ 
strument in the illustration. The current being meas¬ 
ured passes down through this suspension wire, 
through the wire of the coil and out by means of a 
spiral spring which is connected to the lower end of 
the coil. A very light mirror attached to the movable 
coil serves as a means to determine the extent of the 
deflection. Either of two methods may be emploved. A 












Instruments for Testing 


249 


lamp and a graduated scale are so arranged that a 
beam of light coming through a slit in a hood over the 
lamp falls on the mirror and is reflected on the scale. 
A telescope may be used in place of the lamp. The 
telescope is focused so that the scale is visible in the 
mirror. The slightest movement of the mirror can 
then be accurately read through the telescope. 

Practically all of the instruments just described are 
made use of only in the laboratory and are not suitable 
for ordinary switchboard and testing purposes. To 
be of commercial use an instrument must not be seri¬ 
ously affected by the earth’s magnetism nor by the 
presence, of large masses of metal or strong magnetic 
fields such as are apt to be found in a dynamo room 
for instance. The instrument must be portable, and 
the accuracy of the indications must not change un¬ 
duly with continued use. The instrument must also be 
easily read and unnecessary calculations avoided. 

Commercial instruments are divided into three gen¬ 
eral classes, those for use on direct current, those for 
use on alternating current only, and those for use on 
either direct or alternating current. In each of these 
three classes instruments are designed for special pur¬ 
poses, such as the mesurement of voltages, measure¬ 
ment of current strength and measurement of elec¬ 
trical power. Although the principles upon which 
these various instruments operate are the same, still 
there are some differences in their construction de¬ 
pending on the purposes to which the instruments are 
to be put, as will be described further on. 

Almost any of the galvanometers previously de- 
Bcribed could be used for the measurement of direct 


250 


Operating and Testing 




current voltages, but, for the reasons already assigned, 
most of them are impracticable for general use. 

In Figure 154 is shown the well known Weston in¬ 
strument. A permanent magnet M, constructed of a 
specially prepared steel having the property of retain¬ 
ing its magnetism for an indefinite time, is fitted with 
soft iron pole pieces. In the space between the pole 
pieces, held in place by a non-magnetic metal such as 
brass, is a soft iron core. A coil of fine copper wire 
wound on a copper form is movable in the air gap be¬ 
tween the inner core and the pole pieces. In order 




-O O- 

Figure 154 


that the resistance to turning due to friction be re¬ 
duced to a minimum the coil rests in jewel bearings. 
Two flat spiral springs, one above the coil and one be^ 
low it, serve the double purpose of providing a torque 
against which the coil must act and also carry the 
current to the movable coil. A light pointer fastened 
to the shaft upon which the coil revolves moves over a 
scale graduated in divisions suitable to the purpose to 
which the instrument is put. 

Copper wire being used in the winding of the coil 
some resistance must be connected in series with this 























Instruments for Testing 


251 


coil wffiere the instrument is to be used, to measure 
comparatively high voltages. This resistance is usually 
inserted in the instrument and consists of a resistance 
wire having a very low temperature coefficient, or, in 
other words, a wire of such composition that its re¬ 
sistance will be but little affected by changes in its 
temperature. The importance of using a wire of this 
kind can readily be seen, for, should an instrument 
which had been calibrated at a temperature of 70° be 
used in a room at a temperature of about 100°, the de¬ 
crease in current flowing through the instrument due 
to the increase in resistance in the heated wire would 
seriously affect the accuracy of the instrument. 

The amount of resistance connected in series with 
the coil varies and depends on the voltages which it 
is intended the instrument should measure. In volt¬ 
meters for use on 500 and 600 volt circuits, this resist¬ 
ance is equal to about 65,000 or 75,000 ohms, thus 
allowing a current of about .007 ampere to pass 
through the instrument. 

Current enters the instrument through the binding 
posts and passes through the resistance R, spiral 
springs and the coil. The magnetic field produced by 
the current flowing around the coil acts in conjunction 
with the field of the permanent magnet and tends to 
revolve the coil in a manner similar to that of the 
armature of a motor. As a matter of fact, this meter 
is simply a motor having a permanent field, and an 
armature that can make only a partial revolution. The 
amount of deflection will be proportional to the cur¬ 
rent flowing through the wire of the coil, and as the 
coil always moves in a practically uniform field a uni- 


252 


Operating and Testing 


form scale will result. The movement of the coil is 
restrained by the spiral springs 

This instrument is what is termed “dead beat,’' 
that is, the tendency of the pointer to swing backward 
and forward on deflection is reduced to a minimum. 
The movable coil is wound on a copper frame. When 
on deflection of the instrument this frame moves across 
the field of the permanent magnet, it cuts through 
lines, of force and a current is produced in the closed 
circuit of the copper frame, this action tending to re¬ 
strain the movement of the coil. 

Figure 155 shows a type of instrument similar to 
the one just described but varying in some details. M 



is a permanent magnet fitted with pole pieces of the 
shape shown in the figure, the pole S, S being shaped 
like an iron washer. A coil, C, is attached to a shaft 
which turns in jeweled bearings. A pointer attached 
to the shaft moves over a suitable scale. Current pass¬ 
ing through the coil C causes it to revolve around the 
pole piece S, S. The instrument is made ‘ ‘ dead beat ’ ’ 
by the short circuiting of the copper frame on which 
the coil is wound. 

A type of induction meter which is used only on al¬ 
ternating current circuits is shown in Figure 156. A 
copper or aluminum disc fastened to a shaft, rotates 
in jewel bearings. Projecting over the disc on one 


















* Instruments for Testing 


253 


side and so arranged that the disc rotates between its 
pole pieces is a laminated magnet C, on which is wound 
a coil of wire. Another coil C' is placed so that its 


Figure 156 

field cuts the disc. Both coils are connected in par¬ 
allel. Owing to the fact that with an alternating cur¬ 
rent flowing through the instrument there will be a 
difference in phase in the current flowing in coil C and 



coil C', coil C' having no iron core, a torque is set up 
which tends to rotate the disc, the amount of deflec¬ 
tion being indicated by the pointer attached to the 
shaft. 
































254 


Operating and Testing 


Figure 157 shows in a simplified form an instrument 
which can be used for the measurement of either direct 
or alternating currents. The current to be measured 
is carried through a solenoid S. In the center of the 
solenoid is suspended a soft iron core, which is free to 
move up or down, the motion of the core being regis¬ 
tered by the pointer attached to the supporting arm. 
A counterweight serves to balance the iron core. 

When current flows through the solenoid the iron 
core is drawn down into it, the amount of current 
flowing being indicated by the pointer. 

The principle upon which this instrument operates 
is made use of in a number of different instruments. 
As the action of the solenoid is the same when either 
direct or alternating current is used, this instrument 
may be used on circuits of either system. 

Instruments of the design just described have the 
objection that when used on direct current, with an 
increase in current strength, the instrument will indi¬ 
cate lower than it should, while with a decreasing cur¬ 
rent it will indicate higher. This is due to “hysteri- 
sis” in the iron core, and if the core contains any 
great quantity of iron, makes the instrument value¬ 
less as a voltmeter. With direct current more accu¬ 
rate results may be obtained by first increasing the 
current, then decreasing it and taking an average of 
the readings. On alternating current systems, this 
objection does not exist, but in this case the iron core 
must be laminated to avoid the generation of eddy 
currents. 

The Weston instrument having a permanent mag¬ 
net field cannot be used for alternating current meas- 




Instruments far Testing 


255 


urement. Figure 158 shows the construction of the 
instrument desiged for use on alternating current cir¬ 
cuits. An outer coil C is wound on a circular form. 
Inside of this coil, mounted on jewel bearings, is a 
movable coil C'. Two spiral springs convey the cur¬ 
rent to the movable coil and restrain its motion. The 
two coils are connected in series. When current flows 
through the coils, the movable coil tends to take up a 
position parallel with the stationary coil. When used 
on alternating currents, the polarity of each coil re¬ 
verses at the same time, so that the effect is the same 



as though direct current was used. The instrument is 
damped by a metal vane moving in a partly closed air 
chamber. 

The difference between a voltmeter and an ammeter 
is merely a difference in winding. A voltmeter is 
wound with a very fine wire and registers the differ¬ 
ence in pressure between two wires. The finer the wire 
or the greater the number of turns, the more econom¬ 
ical is the instrument in operation. It needs only to 
produce magnetism enough to deflect the pointer suf¬ 
ficient to admit of accurate calibration. 


















256 


Operating and Testing 


If in any circuit the pressure is greater than the 
range of any accessible meter, several of them may 
be connected in series and the readings of all of them 
added. It is also possible to measure the voltage be¬ 
tween two wires in the manner shown in Figure 159. 
The voltmeter here measures the difference of potential 
around one lamp and if all lamps are exactly the same 
this need be but multiplied by the number of lamps in 
series to obtain the voltage over the whole group. If 
more accurate results are desired, the voltage around 
each lamp may be taken and all of them added. 
Should, however, the lamp at the voltmeter break 



while the meter is connected around it, the voltmeter 
might be quickly burned out. 

There are two classes of commercial ammeters. One 
of these, not extensively used, is cut in series with the 
line and all of the current passes through it. Such 
ammeters have very few turns of wire and are sel¬ 
dom used on heavy currents. The kind in most 
extensive use at present is known as the “shunt” am¬ 
meter. This type of ammeter takes only a small frac¬ 
tion of the current, the bulk of it passing through the 
“shunt.” Such a shunt is shown in Figure 160 and 
the manner of attaching the cords leading to the am¬ 
meter is also shown. The shunt must be designed for 












Instruments for Testing 


25 7 


the particular instrument with which it is to work. 
Nothing must be allowed to disturb the relative resist¬ 
ance of shunt and instrument and the cord sent with 
them should always be used full length, or the read¬ 
ings will be inaccurate. 

The measuring capacity of any ammeter may be in¬ 
creased by providing a suitable shunt. If the resist¬ 
ance of the shunt is made l/9th that of the ammeter,, 
the leadings must multiplied by 10 to obtain the: 
flow of current, if l/99th by 100, or l/999th by 1000.. 

If the capacity of one ammeter is insufficient to 
measure the current, several of them may be con¬ 



nected in parallel, but each must be provided with its 
own shunt. 

Two ammeters must never be connected to one 

shunt. 


WHEATSTONE BRIDGE 

For the measurement of resistances ordinarily met 
with the Wheatstone bridge is generally used The 
principle of its operation, if thoroughly understood, 
will greatly assist in comprehending its uses. 

In Figure 161, a battery is connected in series with 
a resistance AB. If the battery has a difference of 
potential of one volt, and AB has a resistance of 10 
ohms (the balance of the circuit being considered as 








258 


Operating and Testing 


having no resistance) a voltmeter connected across 
from A to B would indicate one volt difference of po¬ 
tential. If the voltmeter is connected between A and 
C, the resistance between A and C being 5 ohms, the 
voltmeter will show y 2 volt. According to Ohm’s law 
E = IR. I, the current, being constant, the voltage 
between any two points must be proportional to the 
resistance between these two points. If the resistance 
between A and D is one ohm, the voltmeter connected 
between A and D would indicate 1/10 volt, while if 
the voltmeter was connected between B and D it would 
indicate 9/10 volt. The resistance of the wire A B 



Figure 161 


might be 20 or 30 ohms, or the battery might have a 
voltage of 10 or 20 volts, the drop over any two points 
on the resistance would, nevertheless, be proportional 
to their resistances. 

In Figure 162, two resistances are connected in par¬ 
allel with each other, and in series with the battery. 
If the voltage of the battery is one volt, that difference 
of potential will be shown by a voltmeter connected 
across A and B. The difference of potential between 
A and any point in the resistance A C B will be pro¬ 
portional to the resistance over which the voltage is 
measured. The same is true of resistance A D B so 











Instruments for Testing 


259 


that for every point in wire A C B there is a corre¬ 
sponding point in resistance A D B of the same differ¬ 
ence of potential. Suppose C and D to be two points 
of equal potential, then there would be no current flow 
over a wire connecting these two points, and a galva¬ 
nometer placed in this wire would indicate nothing. 
The resistance of A C will then be to the resistance of 
B C as the resistance of A D is to the resistance of 
D B. or calling these resistances b, x, a and r respect- 


1 —I 1 — 

Figure 162 

ively we have the proportion a -r r = I) -f x. This ex* 
pression may be written 

— = —, then x = — r 
r x a 

A diagram of the connections of the Wheatstone 
bridge is shown in Figure 163, a and b are the pro¬ 
portional arms, while r is the known resistance and x 
the unknown, or the resistance to be measured. The 
battery is connected across A and B while the galva- 










260 


Operating and Testing 


nometer is connected between C and D. Both battery 
and galvanometer circuits are provided with keys and 
are normally open. 

In the type of bridge shown, the resistances are con¬ 
nected between brass strips, brass plugs inserted in the 
holes between the strips short circuiting those resist¬ 
ances wdiich are not used. In each of the proportional 
arms a and b one plug is always left out. 

To measure an unknown resistance, proceed as fol¬ 
lows: Connect the resistance to be measured across 
the terminals at X. Leave unplugged one resistance 

A __. 


D 


B 

Figure 163 

in each of the arms a and b. If it is known that the 
resistance of the apparatus being measured is not less 
than the smallest resistance in r or greater than the 
greatest resistance in r, make the unplugged holes in 
a and b of equal resistance, say 10 and 10, and remove 
one of the plugs in the arm r. Now press down the 
battery key and then the galvanometer key and note 
the direction of the deflection of the galvanometer 
needle. Now either replace or remove some of the 
plugs in r and proceed as before, and note the deflec¬ 
tion. If the deflection is in the opposite direction the 
















Instruments for Testing 


2 til 

value of the unknown resistance must lay somewhere 
between these two, and if the deflection is in the same 
direction as before, note the extent of the deflection, 
if greater too much resistance has been plugged in and 
if less, too little. Repeat these operations until no 
deflection is obtained. The total amount of the un¬ 
plugged resistance in r will then be equal to the re- 
‘"stance being measured, for 

b b 10 

x = — r, where — = — 1 
a a 10 

If the resistance or the apparatus being measured is 
such as not to come within the limits of the resistance 
in arm r, the unplugged resistance in one of the pro¬ 
portional arms a and b must be varied. If x is large 

b 

as compared with r, then from the formula x = — r 

a 

we see that b must be made greater than a. If 10 ohms 
is unplugged in the a arm and 100 ohms in the b arm, 
then the unknown resistance x will be 100/10, or ten 
times the resistance in r. On the other hand, if x is 

b 

small as compared with r, then — must be small. With 

a 

ten ohms unplugged in b and 100 ohms in a. x would 
be 10/100, or 1/10 of r. 

When balance is obtained, the position of the battery 
and galvanometer could be reversed without changing 


262 


Operating and Testing 



the indication of the galvanometer. In using the 
bridge the battery key should always be depressed 
first, for in measuring a resistance containing induct¬ 
ance or capacity such as a long lead covered cable or 
a circuit containing magnets, if the galvanometer key 
is depressed first and the battery key afterward, a 
deflection might be obtained on the galvanometer even 
with the resistances balanced, this being due to the 


fact that inductance or capacity in the circuit tend to 
momentarily hold back the current so that it requires 
some time to come to its full value. 

One form of Wheatstone bridge known as the Queen 
Acme testing set, which is in very common use, is 
shown in Figure 164 with a diagram of connections 
shown in Figure 165. A galvanometer and battery 
form a part of this set so that the instrument is com¬ 
plete in itself. A number of round brass blocks 


Figure 164 































Instruments for Testing 


263 


mounted on a hard rubber base form the terminals of 
the various resistance coils, as shown in Figure 164. 
Brass plugs inserted in the openings between these 
blocks short circuit the resistance coils so that only 
those coils are in use on which the plugs are removed. 
The middle row of blocks form the two proportional 
arms corresponding to A and B, Figure 165, while 
the upper and lower arms form the resistance R. 

The resistance to be measured is connected between 



% 

the posts marked X. The battery circuit is normally 
open, being closed by the key B. The galvanometer 
key is also normally open, being closed by the key 
marked G. When this latter key is released it makes 
contact with the point shown above the key, this short- 
circuiting the galvanometer winding. This action 
tends to stop the swinging of the needle and makes it 
come to rest quickly. Six chloride of silver cells are 
provided in a sealed metal case. Connection is made 


























264 


Operating and Testing 


to the cells by means of small plugs fitting over pins 
which are connected to the separate cells. By this 
means the battery strength can be varied for various 

The galvanometer is of the permanent magnet type, 
having a movable coil. 

One particular feature of this bridge is the method 
of reversing the proportional arms A and B. This is 
more clearly shown by reference to the diagram, Fig¬ 
ure 165, which shows a simplified diagram of the con¬ 
nections of the bridge. The two proportional arms are 
provided with different resistances, A having 1, 10, 
and 100, while B has 10, 100, and 1,000. With the 
plugs inserted between A and R and B and X arm 
A is placed in series with R and arm B with X. The 
resistance of X will now be 

B 

X = —R 

A 

With the plugs placed in the other two holes, be¬ 
tween R and B and A and X the above arrangement 
is reversed or 

With the lowest resistance in A, 1 ohm, and the 
highest resistance in B, 1000 ohms X will be 1000 
times R for the first positon and 1/1000 of R for the 
second position, so that for measurement of high re¬ 
sistances the plugs should be placed as shown in the 




Instruments for Testing 


265 


diagram, while for measurement of low resistances the 
plugs should be placed in the opposite noles. With a 
single plug inserted between R and X, the instrument 
may be used as a straight resistance box, the connec¬ 
tion being made between the posts X. 

MAGNETO 

The magneto is used for testing purposes where an 
approximate determination of the insulation resist¬ 
ance or a test as to continuity of a conductor is de¬ 
sired. This piece of apparatus is a simple form of 
alternating current dynamo. The fields are formed by 
permanent steel magnets, while the armature is made 
of soft iron, the wires being wound through two slots 
running parallel with the axle. The armature wind¬ 
ing consists of one coil of a considerable number of 
turns of fine wire. One end of this coil is directly 
connected to the metal frame of the magneto, while 
the other end is connected to an insulated pin running 
through one end of the shaft. 

By means of a crank connected to a gear wheel work¬ 
ing in a pinion on the end of the armature shaft, the 
armature is turned at a high speed. As the armature 
revolves an alternating current is generated flowing in 
one direction during half a revolution of the armature 
and in the reverse direction during the balance of the 
revolution 

A polarized bell is connected in series with the mag¬ 
neto armature. A ring may be obtained with the ordi¬ 
nary testing magneto through a resistance of from 
25,000 to 50,000 ohms, the capacity of the magneto de¬ 
pending on the strength of the permanent magnet, 


266 Operating and Testing 

number of turns of wire on the armature and the speed 
at which the armature is revolved. 

In testing lead covered wires or cables, a ring is 
sometimes obtained even when the line which is under 
test is clear. This effect is due to the lead covering of 
the cable which causes it to act as a condenser, becom¬ 
ing charged as current from the magneto flows into 
the wire and then discharges back through the bell 
magnets. The same effect may be produced in testing 
lines installed in iron pipe. In this case the action is 
as follows: When current from the magneto flows 
into the wire lines of force are produced in the space 
around the wire, these lines of force being greatly in¬ 
creased by the presence of the iron pipe. As the cur¬ 
rent ceases to flow into the pipe these lines of force 
close in on the wire and produce a current in the op¬ 
posite direction to the original current. 

These effects are generally obtained on long runs of 
wire only so that for the ordinary test the magneto 
will indicate correctly. 

TELEPHONE RECEIVER 

One of the most convenient devices for ordinary 
testing purposes consists of a telephone receiver con¬ 
nected in series with a few cells of dry battery. An 
outfit of this kind is easy to make, and has the advan¬ 
tage of being small and easy to carry about. The out¬ 
fit generally consists of what is known as a “watch 
case” receiver connected to two small cells of dry 
battery. Flexible cords of suitable length are pro¬ 
vided with clips at the ends. A permanent connection 
can be made with one terminal and the other used for 


Instruments for Testing 


267 


testing. The outfit is very light and can be easily car¬ 
ried in the pocket. 

This apparatus has several advantages over the 
magneto. A test can be made in much less time as the 
necessity of turning the magneto is avoided. The tel¬ 
ephone receiver being more sensitive than the magneto 
bell, the approximate resistance can be more readily 
ascertained. In fact, with a little practice one may 
become so accustomed to the “click’’ as to be able to 
determine very closely the insulation resistance. In 
using the apparatus in this way, contact should be 
made by simply “tapping-’ the wire which is being 
tested. The connection should never be left on for 
any great length of time, as the battery will weaken 
and the click will be reduced. 

In testing for insulation resistance with a magneto, 
or in fact, any of the common methods in use for this 
purpose, the condition of perfect insulation is shown 
by no indication on the testing apparatus; for in¬ 
stance, no ring with the magneto. The same indica¬ 
tion would be obtained if the apparatus was defective, 
or if the wires connected to the apparatus were broken 
so that one is never certain when no ring is obtained 
on the magneto bell that the wire being tested is 
clear. 

With the battery and receiver a click will be ob¬ 
tained on nearly all tests, even though the insulation 
resistance is very high so that one can always be sure 
that the apparatus is working properly. 

In testing a lead covered cable or wires in conduit, 
the condenser effect due to the lead covering will cause 
a click even where the wire which is being tested is 


268 


Operating and Testing 


clear. This may be overcome by making a succession 
of contacts, the first contacts charging the lead cover¬ 
ing and the succeeding contacts indicating the condi¬ 
tion of the wire. 

In making up an apparatus of this kind, it is well to 
have some means of opening the battery circuit when 
not in use, so that the battery will not short in case 
the ends of the flexible cords should come together. 



CHAPTER XIX 


TESTING DYNAMOS AND MOTORS 

The usual tests to be made on dynamos are: 
Insulation resistance. 

Rise of temperature. 

Regulation. 

Efficiency. 

The insulation resistance is easily measured by a 
voltmeter attached to a circuit, as shown in Figure 166. 



Figure 166 


If there is any indication of current, the insulation is 
defective. The voltage used for this test should be 
equal to that for which the dynamo is intended. Very 
often such an indication is due to dampness and the 
machine may be cleared up by running it for a while 
with a strong current that will cause the wiring to 
heat up considerably. This must not be attempted if 
the voltmeter indicates a serious defect. 


260 

















270 


Operating and Testing 


The formula for use in connection with a voltmeter 
when the exact amount of the resistance is desired to 
be known, is: 

y—V' | 

Xr=R- 

V 

Where V is the full voltage of battery or other 
source of current and V' the reduced reading obtained 
through the voltmeter and the resistance to be meas¬ 
ured, and R the resistance of the voltmeter. 

To determine the temperature rise, the machine 
must be run for some time with the full current for 
which it is designed. Small machines often attain 
their maximum temperature in five or six hours, 
larger ones must be run longer. It is always advisable 
to continue the test as long as there is any noticeable 
increase in temperature from time to time The test 
is made by placing a suitable thermometer upon the 
frame of the machine and covering it with waste so 
as to eliminate the cooling influence of the air. As 
an undue rise of temperature causes the most harm to 
the windings, it is to these that the thermometer 
should be applied and in such a location that the high¬ 
est temperature produced in any accessible place will 
be recorded. 

Roughly a temperature rise of about 60 degrees 
above the surrounding atmosphere may be allowed but 
if the machine is to operate in a very hot room, a lesser 
allowance must be made. Very few insulations will 
stand a temperature higher than 150. 

To test the regulation of a machine it should be 




Testing 


271 


run with loads varying from 0 to the full load. The 
greater the drop in voltage within these limits, the 
poorer is the regulation of the machine. If a com¬ 
pound wound machine is to be tested in this manner, 
the compound winding must be short circuited so that 
it will have no effect upon the voltage. After the fore¬ 
going test has been made, the compound winding may 
be placed in service and another test made to deter¬ 
mine the regulation with this winding in action. 

While this test is being made the action of the com¬ 
mutator may also be noted. A change in load, of 
course, brings with it a necessary change in the posi¬ 
tion of the brushes. This should not be very much, 
however, as the machine will be troublesome to 
handle. 

The regulation test with motors is simply a test for 
variation in speed with changes in load. The load 
may be placed upon the motor by means of the Prony 
brake arrangement, shown in Figure 168, or by ar¬ 
ranging to have the motor drive a dynamo as illus¬ 
trated in Figure 167. In this test the change in volt¬ 
age of the line supplying power should be taken into 
consideration. If there is much resistance in this line 
there will be considerable drop in voltage and this will 
cause a slackening off in speed. 

A well designed shunt motor at the terminals of 
which a constant E.M.F. is maintained should not 
drop off more than 10 per cent in speed from no load 
to full load. 

• Figure 167 shows the connections for testing dyna¬ 
mos and motors without the expenditure of much en¬ 
ergy. The motor M drives the generator G and the 


272 


Operating and Testing 


current from it is pumped back into the line. The 
actual energy absorbed and lost in the test is only that 
which is taken up to overcome the friction and the 
losses in the two machines. This arrangement for ob¬ 
taining a load can be used for any of the tests previ¬ 



ously described. The power consumed by the two is 
found by multiplying the volts and amperes used by 
the motor. 

The power delivered back to the line is equal to the 
product of the volts and amperes in the generator cir- 
























































































Testing 


273 


cuit. Roughly the efficiency of the two is the load on 
the dynamo divided by the power delivered to the 
motor. 

In order to obtain the efficiency of the generator, 
we must first, have the efficiency of the motor. If the 
two machines are similar, either motors or generators 
it will probably be accurate enough to assume that 
half the loss occurs in each machine. 

If such is the case, we must take the square root of 
the combined efficiency to obtain the efficiency of the 



Figure 168 

single machines. Thus, if the efficiency of the two ma¬ 
chines is .81, the efficiency of either machine singly 
will be .90. 

The efficiency of a motor may be tested by means 
of the well known Prony brake shown in Figure 168. 
In this figure P is a pulley attached to the shaft of 
the motor. The lever L is fastened to the pulley by 
means of the block and the thumb screws. When 
the motor is in motion the screws must be so tight¬ 
ened that they will allow of rotation of the armature 
shaft sufficient so that the motor may be taking the 
current at which it is to be tested. The spring scales 














274 


Operating and Testing 


are provided to measure the force with which the 
motor acts upon the lever. 

In order to learn the power delivered by the motor 
we must know the length of the lever from the center 
of the pulley to the scale. The number of pounds reg¬ 
istered on the scales and the speed of the pulley in 
revolutions per minute. The product of these factors 
divided by 33,000 will give us the H. P. delivered by 
the motor. 

The products of the volts and amperes maintained 
at the terminals of the motor while the foregoing ob¬ 
servations were made will give us the H. P. consumed 
by the motor and the H. P. delivered divided by the 
H. P. consumed will give us the efficiency of the mo¬ 
tor. 

In connection with alternating current motors the 
volts and amperes at the terminals of the motor must 
be multiplied by the power factor. The power factor, 
however, varies with the load on the motor and other 
line conditions and will generally have to be guessed 
at unless a power factor indicator is at hand. 

The above test is usually made at full load. If the 
losses at no load are required we need but take the 
produce of the volts and amperes when the motor is 
running empty. 

The loss in the fields of a dynamo or motor may be 
made exceedingly small or may take up nearly the 
whole output of the machine. From time to time 
cheap motors are brought out that require almost as 
much energy to excite their fields as is required to do 
the work. A test of the field losses can readily be 
made by measuring the current flowinsr in them. This 


Testing 


275 


should not be much over 5 per cent of the capacity of 
the motor for medium sizes. 


CIRCUIT TESTING 

Figure 169 can be used to illustrate the principles 
which underlie the testing for trouble on series are 
or incandescent circuits. The principal troubles en¬ 
countered on such circuits are due, either to an open 
circuit, or to one or more grounds. If more than one 
ground exists and if those grounds are “good,” they 
will cut out a number of lamps and for that part of 
the circuit amount to the same thing as though a 
short circuit existed on a multiple circuit. If, for in- 



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Figure 169 




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stance, two good grounds exist as shown at B and C, 
they will have the effect of cutting out the lamps 
shown at the right, the current passing through the 
low resistance of the ground rather than through the 
lamps. 

Sometimes, however, such grounds are not very 
good and then they merely rob the lights of part of 
the current; at other times such grounds are inter¬ 
mittent and due to wires swinging against wet trees 
or buildings, or the jarring of railroads, etc., which 
cause bare parts of the wires to come in contact with 














276 


Operating and Testing 


grounded parts of structures. So long as there is 
but one ground on a system no harm can result be¬ 
cause this can establish no circuit through which cur¬ 
rent can flow. But when the second ground appears, 
there is sure to be trouble, and furthermore the ex¬ 
istence of one ground makes the appearance of a sec¬ 
ond far more likely because the resistance from pole 
to pole through the ground is thereby reduced one- 
half. 

If one ground exists, the repair man or operator, if in 
connection with the ground will, when he touches the 
wire, at once establish the second ground and cause 
more or less current flow through his body. It is, 
therefore, of the utmost importance from every point 
of view to detect grounds as soon as they come on to a 
system. For this purpose every plant should be 
equipped with a ground detector as elsewhere described 
and frequent tests should be made with it. 

If a ground has been noted on the line, the best way 
to locate it is the following: Cut off the current, leave 
the circuit open, and place a temporary ground on one 
of the wires at the station; then go out along the line 
and at some convenient place open the circuit of that 
wire on which the temporary ground is placed. In¬ 
sert into the circuit any of the testing instruments 
previously described. So long as an indication is ob¬ 
tained it shows that you have cut into the circuit be¬ 
tween the two grounds; when no further indication 
can be obtained the ground has been passed; thus, sup¬ 
pose the ground to be located is at B, Figure 169, and 
the temporary ground at A; if the testing set is in¬ 
troduced at D, there will be an indication of current, 


T esting 


277 


while when it is placed at E there can be none. If 
the line has been closely watched, it is very unlikely 
that more than one ground will come on suddenly but 
in case of an old line that has been neglected and in 
the event of a heavy rainstorm, it may be possible 
that several grounds appear together. If the condi¬ 
tions make this appear as likely, it will be well to cut 
the line into sections and see which parts are clear 
as the above test will be very confusing if more than 
one ground should exist at the same time. 

If the line cannot be cut dead long enough to locate 
the ground, there are two ways in which the ground 
can be located. One method which may be used if the 
ground on the line is good and if there is no danger 
from fire, consists in putting a second ground onto 
the system and noting which lamps are thereby cut 
out of the circuit. Thus, if as in Figure 169 the 
ground to be located exists at B and a test ground is 
put on at A, all of the lamps between A and B will 
be cut out and will show that the ground is somewhere 
between the two lamps, on either side of B. 

In place of the foregoing, connections may be made 
as shown in Figure 169, at the left. Here the little 
circles represent a series of 100-volt incandescent 
lamps (each lamp requires twice the voltage of one 
of the arcs), which by means of the throw over switch 
S may be connected to either side of the circuit. G is 
a ground permanently connected at the last lamp in 
the series. These lamps as connected virtually meas¬ 
ure the difference of potential which exists between 
the point on the line at which the ground is located 
and the location of the ground at the lamps. If. with 






278 


Operating and Testing 


a ground located at B, connection is made by the 
throw over switch to the positive wire, there will be 
only the difference of potential due to four lamps 
which will cause the incandescent lights to burn, while 
if connection is made to the negative wire there will be 
a difference of potential equal to eleven arc lamps 
which will manifest itself on the incandescent lights. 
By means of the flexible wire shown in dotted lines, 
some of the lamps can be cut out until those remain¬ 
ing in circuit burn at full candlepower. If the volt¬ 
age of the incandescent lamps is as indicated above, 
twice that of the arcs, then for every incandescent 
lamp burning at its proper candlepower, there will be 
two arc lamps between the station ground and the one 
on the line; in the case as shown in diagram, if con¬ 
nection is made to the upper wire, two incandescent 
lamps will burn properly while with connections made 
to the lower wire, five will bum. 

To locate open circuits it is also of advantage to 
place a ground on one side of the line, at the station 
as at A. Now go out on the line and test back to this 
ground, of course, grounding the instrument you have. 
As long as you are located between the open place arid 
the station, you will get an indication; when this place 
is passed no further indication can be obtained. 

In connecting up arc lamps, it is best to begin at 
one end of the circuit, determine whether this is to be 
positive or negative, and connect the first lamp accord¬ 
ingly. Now ground that end of the circuit and pro¬ 
ceed to the next lamp on that leg. If the wires are 
run overhead, there will be no difficulty in tracing the 
wires, but if they are underground there will be two 


Testing 


279 


ends visible, and it must be determined which of these 
is to go to the positive and negative poles of the lamp. 
By grounding the end from which the start was made 
it will be easy to test back and find the leg which 
comes from the lamp first connected. 

The finding of grounds on multiple circuits is a 
much simpler matter. Such systems are always sub¬ 
divided into branch circuits so that no great amount 
of wiring is ever dependent upon a single fuse, and 
by these fuses any part of the wiring can be readily 
separated from the rest. A ground having been dis¬ 
covered on such a system, it becomes necessary to dis¬ 
connect different centers until the one containing the 
ground is found. When so much is accomplished the 
branch circuits are next disconnected until the proper 
one is found. After this, if the wiring is open, an in¬ 
spection will reveal the exact location, if the wiring 
is concealed it may further be necessary to disconnect 
parts of the circuit until at last the section containing 
the trouble is found. 

With multiple circuits a broken wire always indi¬ 
cates very nearly its exact location, so that it can eas¬ 
ily be found by inspection. If, for instance, in Fig¬ 
ure 170, the wire is broken at E, the seven lights at 
the right will not burn, while those at the left will not 
be interfered with; if only the wire at F is broken 
only one light will be out. 

A new system of incandescent lighting is best tested 
circuit by circuit. By testing for ground over a 
whole installation at once, there is always the chance 
that some of the fuses may not make proper connec¬ 
tion (especially with cartridge and plug fuses) there 


280 


Operating and Testing 


is also a likelihood that some of the switches may be 
left open; either of these conditions would make the 
test very unreliable. When each circuit is tested by 
itself the testing instrument can be connected to the 
binding posts of the cut-out, or at any socket in the 
circuit, wherever it is most convenient to obtain a 
ground connection for the instrument. Unless lamps 
are installed in the sockets each leg must be separately 
tested, and if switches do not indicate whether on or 
off, the test should be made with the switch in two po¬ 
sitions, one of which is sure to be on. With most snap 
switches it is, however, easy to determine by the 





sound of the snap whether the switch is closed or open. 

The next test to be made is for short circuit. If a 
good instrument is connected at C and D and a short 
circuit exists, it will at once cause an indication. If 
there is no such indication, we may proceed to test 
for continuity. For this purpose the testing instru¬ 
ment may be left at the cut-out and connection made 
at each socket with a screw driver or anything else by 
which the opposite poles can be brought together so 
as to obtain an indication on the test instrument. 
Where plug cut-outs are used, a lamp screwed into 
one of the receptacles of the cut-out is about the only 
test instrument needed except when testing for 
grounds. 

In connection with three wire circuits, it is custom- 











Testing 


281 


ary to run the neutral wire in the center, but one must 
not always rely upon this being'the case. It is very 
important to have these wires properly connected, as 
a wrong connection will result very likely in the de¬ 
struction of a large number of lamps, and possibly in 
causing a fire. If the neutral wire on the system is 
grounded there are two ways by which it can be found. 
The simplest method, requiring only one lamp, is to 
connect this lamp to ground and to the wires one by 
one, when connected to either of the outside wires the 
lamp will burn at full candlepower, while when con¬ 
nected to the neutral it will not burn at all. The 
other method requires two lamps but no ground con¬ 
nection, and on this account is the most used. Con¬ 
nect two incandescent lamps of the proper voltage in 
series and try the wires, two at a time; when the posi¬ 
tive and negative wires are found, the lamps will burn 
brightly, while in connection with the neutral they 
will be at less than half candlepower. This test is 
also often made by touching the wires with the fingers 
where the voltage is not over 220 and determining by 
the severity of the shock which are the two outside and 
which the neutral wire. 

If it is desired to learn which is the positive or neg¬ 
ative wire, the test can be made by inserting ends of 
wire connected to the two poles of the circuit through 
some water contained in a small cup (non-conducting 
material preferred). The negative pole will be indi¬ 
cated by the formation of small bubbles of hydrogen 
gas near the w T ire. If a metal cup is used for this test, 
there is, of course, danger of a short circuit if the 
wires come in contact with the metal. 


282 


Operating and Testing 


In Figure 171 we explain the testing out for the 
connection of a pair of three-way switches. It is as¬ 
sumed that the wires are run in conduit and nothing 
but the ends of the wires in the three junction boxes 
are visible. The switches are to be located at 1 and 2 
and the lamp to be controlled by them at 3. First find 
which are the feed wires, in this case 4, and bend them 
out of the way; now at each of the switch outlets take 
any two of the three wires and twist the bared ends 
together and proceed to the light outlets, and by test¬ 
ing find the two short circuits thus made and perma¬ 
nently connect these two sets of wires together. Con- 



Figure 171 


nect the lamp to the remaining pair at this outlet and 
at 1 connect the single wire coming from 3 to one of 
the feed wires. The remaining feed wire now goes 
to that pole of the switch which is in direct connec¬ 
tion with the line, and the other two are connected to 
the other binding posts. The other switch outlet is, 
of course, connected in the same w r ay. 

Figure 172 will help to illustrate the method of 
testing out a circuit of incandescent lighting for the 
purpose of making the final connections. We begin 
by placing some testing instrument and battery at the 
cut-out and connecting it to the circuit as at T. Now 
proceed to one of the outlets and baring the ends of 
wires found there, bring the different ends temporar- 












Testing 


283 


ily together until two wires are found that cause an 
indication on the testing instrument. The most con¬ 
venient instrument for this purpose is an ordinary 
call bell and battery, as it can be heard throughout 
different rooms. After the wires coming from the 
cut-out have been found, ends at other outlets may 
be temporarily connected together as, for example, at 
L and we now again try different wires in connection 
with the pair found until a ring is obtained which in¬ 



dicates that we have found the wires thus connected 
together. In this manner by proceeding from outlet to 
outlet the meaning of every wire can be determined 
and connections made as required. As a precaution 
before beginning to test out in this manner, it will be 
well to separate all wire so there may be no accidental 
short circuits, which would cause confusion. 

Three tests should be made on every fixture before 
it is installed, and for these tests sensitive instruments 
should be used, or a voltmeter and the pressure of the 
lighting system. The first test may be for short cir¬ 
cuit in the wiring and for this purpose connections 













284 


Operating and Testing 


are made as shown in Figure 173. If this test shows 
clear the connections may be left as they are and a 
test for continuity made by inserting a screw driver 
or other piece of metal into each socket so as to com¬ 
plete the circuit through the voltmeter and cause an 
indication. If all sockets are found perfect, the test 
for contact with the metal of the fixture may be made 
by disconnecting one of the wires, say 3, and bringing 
it in contact with the metal of the fixture while the 



disconnected fixture wire is connected to the other 
wire of the voltmeter at 2. 

A circuit can be tested for loss in the following man¬ 
ner: With a voltmeter measure the voltage at the 
supply end of the line, and also at the center of dis¬ 
tribution or at the motor, as the case may be. The 
reading will always be greater at the supply end and 
the difference between the two will be the loss in volt¬ 
age. In order to find the percentage of loss in the line, 
we divide the volts lost by the volts at the supply end. 

The loss varies with the current and is inversely 








Testing 


285 


proportional to it. In order, therefore, that the test 
may be of value, it must be arranged that at the time 
of test the average current be in use or if this is not 
practicable, the current flowing at the time of test 
must be known. The average loss will be in the same 
proportion to the loss indicated as the average current 
is to the current flowing at time of test. This cur¬ 
rent multiplied by the volts at the supply end of the 
line, will give the total watts delivered at this point, 
and this multiplied by the percentage of loss will give 
the total watts lost. 

Instead of making the above test with a voltmeter, 
it can be calculated if the size of the wire used is 
known. The loss in voltage is equal to the current 
multiplied by the resistance, and, therefore, if the re¬ 
sistance is known, we need but multiply with the am¬ 
peres to find the loss in volts. In the table below the 
loss in volts per 100 ampere feet (length of run, one 
leg, X current) is given to facilitate these calcula¬ 
tions. The loss in volts is the same, no matter what 
the voltage of the system may be but, of course, the 
percentage of loss which the actual loss represents 
differs with the voltage of the system; thus, a loss of 
514 volts corresponds to a loss of 5 per cent at 110 
volts, but only 2 y 2 at 220. 


B. S. gage. 

14 _ 

12 . 

10 . 

8 . 

6 . 


Loss in volts 
per 100 amp. ft. 

.53 

.33 

.21 

.13 

.08 







286 


Operating and Testing 


4 . 

3 . 

2 . 

1 . 

0 . 

00 . 

000 
0000 


.052 

.04 

.03 

.026 

.02 

.016 

.013 

.01 


To find the loss in any line by the use of this table; 
multiply the current by the length of one leg of the 
line and divide by 100. Use the product so obtained 
to multiply the loss given in the table, the result will 
be the total loss in volts in the line. 

If the size of wire in any installation is not known, 
the best and simplest manner wherever practicable 
to determine it is with a wire gage. Such a gage is, 
however, not always at hand and in connection with 
wires already installed, often cannot be used without 
cutting into the insulation. 

Below is given a table by which the gage number 
of wires can be quite approximately determined from 
outside measurements. Although these measurements 
are not perfectly correct, they will not be found suf¬ 
ficiently inaccurate so that any very great errors will 
be caused thereby. 

The circular mils contained in any wire can be 
found by multiplying the diameter of the wire ex¬ 
pressed in thousands of an inch by itself. If the wire 
in question is stranded, the square of the diameter 
must be multiplied by .75, this will give quite approx¬ 
imate results although not quite accurate. 












Testing 


287 


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TESTING FOR, AND PREVENTION OF ELECTROLYSIS 

The damage due to currents of electricity passing 
from the grounded part of the structure and rails of 
any system of distribution, such as a street railway 
line for instance, depends entirely upon the relative 
resistance of the metallic return circuit afforded by 
the structure and whatever auxiliaries may have been 




























































288 


Operating and Testing 


provided and the resistance of the earth in the vicin¬ 
ity of the structure. 

There are but two ways in which this action can be 
lessened or prevented, the insulation of gas and water 
pipes being considered impracticable One of these 
methods consists in providing a metallic return cir¬ 
cuit of very low resistance so that only a very small 
amount of current will escape from it. With this 
method the amount of copper required is large and 
varies with the conductivity of the earth return in 
different places. At best it can only mitigate the evil 
since no amount of copper can ever entirely prevent it. 

The other method consists in bonding all pipes and 
other metallic bodies that are underground in the 
vicinity of the structure to the structure in such a 
way that current can pass to and from them without 
doing any damage. This latter method, of course, in¬ 
volves also the bonding of all pipes at all joints. If 
this is not done, it will aggravate the trouble rather 
than lessen it, since the various bonds might conduct 
a large quantity of current to a certain pipe which 
might be a very good conductor with exception of one 
joint, for instance, and at this joint the greater part 
of the current would pass from the pipe to earth and 
oack again, thus rapidly causing serious damage. All 
of the damage occurs where the current leaves the 
pipes, and if it is not possible to make the piping a 
part of the return system as above described, the next 
best thing will be to protect those points where the 
current leaves the pipes. 

To determine how this can best be done, comprehen¬ 
sive tests should be made. With a voltmeter which 


Testing 


289 


will indicate the direction of the current, readings 
should be taken at a number of places, the more the 
better, from the structure or rails to accessible parts 
of gas and water pipes near the structure. The pres¬ 
sure and direction of current should be noted so that 
complete map of the system can be made from it. This 
being done, a map of the piping along the line of the 
railway should be provided, and the two combined in 
such a way as to show the exact relative position of 
pipes and leaks. In addition to this careful tests of 
the bonding of the structure should be made, and any 
bad spots marked upon the map. The map will now 
reveal quite approximately the relations existing be¬ 
tween the structure and the earth, pipes, etc. The 
current flowing between structure and piping cannot 
be measured, but may be estimated. 

If high pressure towards a pipe is found to exist 
and at the same time the pipe is very close to the rails, 
it would indicate a large current. The same pressure 
with the pipes farther away would suppose a smaller 
current. Again the high pressure might be caused 
by one or a few bad bonds. If the structure is 
perfect, and the pipe lines are also in about the same 
condition throughout the route, a maximum pressure 
from the rails to pipes will be found at the far end, 
and this will gradually decrease toward the middle 
and will from there on be in the opposite direction, 
from pipes to rails toward the power house. No atten¬ 
tion need be paid to current passing from the rails. 
The endeavor must be to intercept the current where 
it leaves the pipes, especially where large currents are 
indicated. Unless the pipe line can be bonded through- 


290 


Operating and Testing 


out, nothing that would lessen the resistance between 
structure and pipes should be installed, because this 
would increase the current. It would, therefore, seem 
to be advisable to connect suitable ground plates to 
the pipes where current leaves them, so that the elec¬ 
trolytic action would take place on these instead of on 
the pipes. If, however, the pipes are very close to 
the rails, the bonding to the structure would not af¬ 
fect the total resistance of the earth return much, and 
would, therefore, be preferable. In many places cur¬ 
rents will be at different times found to be in different 
directions, so that all tests should be made to extend 
over some time. 



Figure 174 


With conditions as shown in Figure 174, where the 
bad bond is indicated near the pipe, a train using cur¬ 
rent at G would cause current to flow from the rail 
to the pipe at the far end and from pipe to rail at the 
left of the bad bond. A train using current at F would 
cause a flow of current in the opposite direction. So 
long as the pipe is near the rails, it will always receive 
some current. 

Tests should be made during that part of the day 
when the load is most evenly distributed. This will 
be at the busiest time. The pressure will vary with the 
currents used in the vicinity at time of testing. The 
















Testing 


291 


voltmeter used in testing is connected from the rails 
to the pipe. It is preferable to have a double scale 
voltmeter, which will also indicate the polarity, but 
this is not essential. If no reading is obtained at a 
certain place, with the wires connected one way, they 
may easily be reversed and the polarity noted on the 
map. 

In Figure 175 a common method of testing bonds is 
illustrated. An ordinary milli-voltmeter is used and 
about 50 feet of No. 20 wire are inserted in each of the 
leads, as indicated in the diagram. This will give a 
resistance of about i/ 2 ohm. The two wires nearest 



Figure 175 


the voltmeter in the diagram are permanently fast¬ 
ened to bridge the bond, and the other wire is moved 
back and forth on the adjoining rail until a spot is 
found at which the voltmeter gives no indication while 
current is flowing. The resistance of the bond is now 
equal to the resistance of the length of rail between 
the other two wires. If any bond shows up much worse 
than the others, it should be attended to. 


PHOTOMETRY 


To measure the efficiency and the candlepower of 
different electric lights is a simple matter and much 
more attention should be given to such measurements 
than is usually accorded them by operators in charge 










292 


Operating and Testing 


of illuminating stations. Thousands of dollars worth 
of fuel is wasted annually because owners and opera¬ 
tors do not understand the loss of energy caused by 
continuing lamps of low efficiency in service. 

There are two very simple methods of measuring 
candlepower; one of these is known as Rumf ord’s, and 
is illustrated in Figure 176. A suitable pencil is set 
up about 2 inches from a wall of light color or a simi¬ 
lar screen. A standard lamp is set up a convenient 
distance from this pencil, so as to cause a shadow from 
it to fall upon the screen. The lamp to be tested is 





then set up in such a manner as also to cause the pen¬ 
cil to cast a shadow upon the same screen but at a 
different angle from the other. It will be noted that 
each lamp illuminates the shadow made by the other 
and that when the intensity of the two lights at the 
screen is equal, the shadows will be of equal darkness. 
The lamps must be adjusted at such distances from 
the screen that both shadows are equal. The candle- 
power of the two lamps is now proportional to the 
squares of the distance that each is from the screen. 
If one is 32 inches from the screen while the other is 
.23, the candlepower of the farther lamp is to that of 




































Testing 


293 


the nearer as 1024 is to 529, or nearly twice as great. 
In order to make this test as sensitive as possible it is 
best to move one of the lamps backward and forward 
in such a way as to be sure that it is a little too far 
in one positon and then a little too close in the other 
and then place it finally in an intermediate positon. 

To measure the power consumed by each of the 
lamps an ammeter and a voltmeter are necessary. If 
connected as in Figure 176 the voltage of both lamps 
will be the same. The current consumed by each lamp 
can be gotten by removing one lamp at a time from 
the circuit, thus requiring only one ammeter. The 
efficiency of the lamp is usually expressed in watts per 


Figure 177 

candlepower. If a certain lamp yielding 20 candle- 
power is taking 58 watts, there will be 2.9 watts per 
candlepower. 

If lamps are to be tested for use on a certain circuit, 
the voltage of that circuit must be applied to them. 
The efficiency and candlepower of incandescent lights 
varies greatly with different voltages. 

Another method, known as Bunsen’s, is shown in 
Figure 177. A piece of blotting paper is soaked at a 
convenient place with oil or grease, so as to form a 
small spot. The paper is then placed between two 
lights and moved to such a position that the grease 
spot does not show. When this position is found, the 





T T T 


<r 


TTT 






























294 


Operating and Testing 


illumination on both sides is equal and the candle- 
power of the two lamps are as the square of their dis¬ 
tance from the paper. 

The illumination obtainable from a lamp varies 
greatly with the angle at which the light is taken, and 
also varies with the shape of the filament. It is fur¬ 
ther often purposely modified by the use of reflectors. 
In the illumination of desks, halls, etc., it is often im¬ 
portant to know how a certain lamp or reflector dis¬ 
tributes the light. For this purpose photometric meas¬ 
urements must be made at different positions under 



the lamp. This can easiest be done by an arrangement 
outlined in Figure 178. The lamp is fastened to a 
strip of wood hinged at one end so that it can be 
placed in different positions from horizontal to verti¬ 
cal through a range of nearly 180 degrees. In the po¬ 
sition shown the light which strikes the pencil or 
grease spot P comes from the tip of the lamp, and is 
the same as would be found directly under the lamp if 
it were hanging. If the lamp is gradually raised 
and the candlepower taken at the different positions 
we can obtain a curve of the illumination throughout 





















Testing 


295 


one whole side of the lamp. At each change of posi¬ 
tion the candlepower must be measured and marked 
off on the radial line in Figure 179 that corresponds 
with the position of the lamp. When all of these have 
been marked, a curve may be drawn combining them 
which will represent the variation in candlepower. 
Such a curve representing half of the illumination 
from one lamp is shown in Figure 179. For this test 



Figure 179 


the board upon which the lamp lies should be painted 
black, so there may be no reflection. 

When comparative tests are made care should be 
taken that the filaments of the lamps tested are about 
alike. An accurate comparison of different lamps re¬ 
quires the taking of complete curves as in Figure 145. 
These will give the average candlepower if properly 
figured up (add all of the measurements and divide 
by their sum) and also indicate whether the lamp is 
suited for the place where it is to be used. 





















296 


Operating and Testing 


The candlepower of arc lamps is often measured by 
means of the dispersion photometer first suggested by 
Prof. Ayrton. The principle of the arrangement is 
shown in Figure 180. The light from the arc is al¬ 
lowed to pass through a dispersion lens which spreads 
it out over a greater area and thus lessens its intens¬ 
ity. 

Sin^e the intensity of light varies as the square of 
the distance it follows that, using a dispersed light, 
we may consider the distance of the lamp from the 
screen as proportional to the square root of the area 



illuminated by the dispersed light. The lens limits 
the quantity of light, and as it is circular we may 
take the diameter of the circle illuminated as the 
square root of the area. The intensity of the light is 
then the same as though the distance from the arc to 
the screen were equal to D divided by L and multi¬ 
plied by A; D being the diameter of the circle of dis¬ 
persed light, L the diameter of the lens and A the 
distance from the arc to the lens. When the shadows 
cast by the arc and the standard lamp at the pencil P 
are equal, the candlepower of the arc is as much 




Testing 


297 


greater as that of the standard I as j A X_ 

\ L 

is greater than E 2 . 

Numerical example: Let A equal 24 inches, L 
equal 2 inches, D 18 and E 12; we have then 24 X 18 
divided by 2 equals 216; this squared equals 46656, 
and this divided by 12 2 or 144 equals 324, which is the 
relative candlepower of the arc over the standard. 



CHAPTER XX 


DYNAMO AND MOTOR TROUBLES 
DYNAMO TROUBLES 

In this chapter the usual troubles occurring in dy¬ 
namos are enumerated in the order in which it is most 
likely they occur. As a rule, time will be saved by 
testing for causes in the order in which they are listed. 

FALURE TO GENERATE 

Cause 1. Poor contact of brushes. This in turn 
may be due to dirty commutator, ragged brushes, in¬ 
sufficient tension on brushes, improper position of 
brushes. A rough commutator, if the dynamo is oper¬ 
ating at high speed, may prevent contact even though 
at rest the connection may appear to be perfect. 

Cause 2. Open circuit in the fields. In arc dyna¬ 
mos, this open circuit may be out in the line some¬ 
where. Poor contact of brushes in series machines is 
equivalent to an open circuit. 

Cause 3. Lack of residual magnetism. Test pole 
pieces with pliers or small piece of iron or steel; if 
there is no attraction, magnetize fields from a battery 
or from switchboard, if accessible. If magnetizing 
with one polarity does not start generation, try mag¬ 
netizing in opposite direction. Sometimes generation 


298 



Dynamo and Motor Troubles 


299 


can be started by striking the pole pieces lightly with 
a hammer. Series dynamos can sometimes be started 
by short circuiting the brushes for a fraction of a sec¬ 
ond by fastening a wire to one of the brushes or ter¬ 
minals and wiping the other end across the other 
brush for the shortest possible length of time. 

Cause 4. With shunt dynamos a short circuit con¬ 
nected to the dynamo will prevent generation entirely. 
With compound dynamos it may do so only to a cer¬ 
tain extent. There will be some magnetism due to the 
series fields, but none due to the shunt. Disconnect 
everything from the dynamo except voltmeter. 

Cause 5. Wrong connection of half of the fields; 
one opposing the other. This can be tested for with 
a compass. If the fields are right, each will attract 
a different end of the needle. Do not bring needle too 
close to either pole piece, or it may be reversed in 
polarity. By short circuiting first one and then the 
other it can also be determined whether both field 
coils are acting in the same direction. The needle 
must be attracted the same way, no matter which coil 
is cut out. 

SPARKING OF BRUSHES 

Cause 1. W T rong position of brushes. The brushes 
should be at the neutral point, and this can be found 
by moving back and forth until the point of least 
sparking is found. With increase of load the brushes 
must be shifted in the direction of rotation of the ar¬ 
mature. When load decreases, the shifting must be 
in the opposite direction. The more modem dynamos 
require very little shifting with changes in load. In 


300 


Operating and Testing 


connection with series arc dynamos the sparking at 
the brushes is unavoidable and special appliances are 
usually provided to take care of it. 

Cause 2. Rough commutator, ragged brushes, or 
dirt on commutator. 

Cause 3. Insufficient tension allowing the brush to 
leave the commutator. 

Cause 4. Brush either too narrow or too wide. If 
too narrow it may leave one commutator section before 
making proper connection with the next. If too 
wide, it will short circuit several of the coils and the 
breaking of this current will manifest itself by spark¬ 
ing. 

Cause 5. Brushes not correctly spaced. In two 
pole machines they should be diametrically opposite 
each other. Except in some special machines they 
should always be equally spaced. 

Cause 6. Changes in load with some dynamos. 

Cause 7. In compound d. c. machines wrong con¬ 
nection of series coils will cause sparking. In com¬ 
pound alternators a wrong setting of the commutator 
will cause sparking. If the load is inductive and 
changing, there must be a constant shifting with 
changes in load to prevent sparking. 

Cause 8. Open circuit in armature. If this is the 
cause of sparking the sparks occur only at one place 
on the commutator and an inspection should reveal 
the location of the break. For exhaustive treatise on 
armature testing and repairing, see “Practical Arma¬ 
ture and Magnet Wiring.*' 


Dynamo and Motor Troubles 


301 


HEATING OF ARMATURE 

Cause 1. Overload. Compare capacity of machine 
with load. The heating increases as the square of 
the current. 

If several machines are operating in parallel, one 
may be running the other as a motor. With compound 
machines the ammeter may be cut into the same side 
as the equalizer and the reading may be altogether 
unreliable/ 

Cause 2. Short circuit in armature coil. This will 
speedily show itself by burning out. A strong odor 
of overheated shellac will be the first indication of 
trouble. 

Cause 3. Defective construction; wires too small; 
foucault currents; hysterisis. 

Cause 4. Poor ventilation. Some types are ar¬ 
ranged so they can be either enclosed or opened at 
the ends. 


INABILITY TO REGULATE VOLTAGE 

Cause 1. Speed too low so that even with all re¬ 
sistance cut out of the regulator the resistance of the 
field circuit is too high to allow sufficient current to 
flow. Fields must be either rewound or connected in 
parallel, and a new suitable rheostat provided. 

Cause 2. Speed too high so that even with all re¬ 
sistance in circuit the voltage is above that desired. To 
remedy this additional resistance must be provided 
unless, of course, the speed can be made correct. 


302 


Operating and Testing 


FIELDS RUNNING HOT 

Cause 1 . Voltage at which machine operates much 
higher than intended. 

Cause 2. Fields connected in parallel where they 
were intended to be in series. 

Cause 3. Part of field cut out either by i ‘ ground ’ ’ 
or improper connection of wires in coil. If this is the 
cause, one of the fields will be abnormally hot and the 
other cool. 

SHOCKS OBTAINED FROM TOUCHING MACHINE 

This is always due to either static electricity or 
grounding of some live part of the system on the 
frame of the machine. Static electricity is caused by 
the belting and can be remedied by providing arrester, 
or the shafting may be grounded. 

To locate ground separate armature and fields and 
test for location. After this, the exact location can be 
found only by inspection and may require unwinding 
of coils. 

SHAFT AND BEARINGS RUNNING HOT 

Improper oiling. Box too tight. Rough bearing 
surface. Bent shaft. Excessive belt tension. End 
thrust due to improper leveling or armature not being 
centered and in consequence possessing a tendency to 
be ‘sucked in,” thus pressing heavily on one of the 
collars. 

MOTOR TROUBLES 

Fuses blow at starting. 

Cause 1 . Fuse may be too small, or contacts may 
be dirty or loose. 


Dynamo and Motor Troubles 


303 


Cause 2. Motor may be overloaded, or stuck fast 
in some way. 

Cause 3. Rheostat may be manipulated too fast. 
As a rule from 20 to 30 seconds should be consumed 
in the starting of the average motors. 

Cause 4. Wrong position of brushes. Brushes 
should be at diametrically opposite points. 

Cause 5. The voltage supply may be higher than 
the motor is designed for. If alternating the frequency 
of the supply may be lower than the motor requires. 
If the frequency is higher, not enough current can be 
obtained. 

Cause 6. There may be a short circuit in the ar¬ 
mature or in the field. A short circuit may be caused 
by two grounds in a two-wire sytem, or by one ground 
in three-wire system with grounded neutral. 

Cause 7. The motor may be improperly connected. 

Cause 8. The field circuit may be open, thus pre¬ 
venting the armature from generating the necessary 
counter E.M.F. 

Cause 9. Light fields, due perhaps to grounded 
wires or short circuit of part of the coils. This will 
be indicated by part of the field running hotter than 
the rest. 


FAILURE TO START 

Fuses do not blow. 

Cause 1. Dead line. Test for current at switch. 
Cause 2. Open circuit in armature or fields, if se¬ 
ries motor. In armature only if shunt or compound 
motor. 


304 


Operating and Testing 


Cause 3. Poor contact of brushes or insufficient 
tension. 

If alternating, frequency of supply may be too high. 
Synchronous motors must be started independently of 
the current. 


SPARKING OF BRUSHES 

See “Dynamo Troubles.” 

Sparking of motor commutator is often much more 
troublesome than with dynamos, because the load 
changes are more frequent and sudden. Since com., 
pound motors are wound with series fields opposing 
or helping the shunt fields, frequently the sparking 
may be due to wrong connection of the fields 

RACING OF MOTOR 

Cause 1. Series motors require constant regula¬ 
tion if connected to variable load. If the load is light, 
motor will speed up. 

Cause 2. Light fields due to improper winding, 
grounds, short circuit or improper connection will 
cause any motor to speed up unless heavily loaded. 
Fields intended to be in parallel may be in series. 
Part of the field winding may be connected to op¬ 
pose the rest. The compound coils may be in opposi¬ 
tion to the shunt coils. In such a case the speed of 
motor will increase with increase in load until if over¬ 
loaded the fields will become so light that finally fuses 
will blow. Strength of field cannot be altered by 
adding or removing wire. It must be rewound with 
larger wire, if field is too light, and with smaller if 
field is too strong. 


Dynamo and Motor Troubles 


305 


MOTOR NOT UP TO SPEED 

Cause 1 . If series motor, it may be overloaded. 

Cause 2. The line supplying current may be so 
long and the wire so small that with a heavy load the 
speed of motor falls off considerably. This condition 
would not affect a motor running light. 

Cause 3. Fields may be too strong. Fields in¬ 
tended to be run in series may be in parallel. In 
such a case they will likely run hot. 

FIELDS OR ARMATURE RUNNING HOT 

See “Dynamo Troubles.” 

MOTOR RUNNING IN WRONG DIRECTION 

Remedy by reversing connections of fields or arma¬ 
ture. If both are reversed, it will have no effect. As 
long as fields and armature polarity remain in the 
same relation to each other, the polarity of the supply 
line is immaterial. 

Multipolar motors and also some bi-polars can be 
reversed by shifting the brushes so that the negative 
brush takes place of the positive. Three-phase motors 
are reversed by changing any two of the wires. Two- 
phase motors are reversed by reversing the wires of 
one of the phases. 

HEATING OF MOTOR 

Cause 1. Overload. 

Cause 2. Voltage too high. 

See, also, “Heating,” under Dynamo Troubles. 

With induction motors one of the phases may be 


306 


Operating and Testing 


out. A three-phase motor will continue to run on one 
phase, but will not start. If such a motor is over¬ 
loaded, it will come to rest and burn out. 

The above includes all of the common troubles en¬ 
countered on ordinary motor circuits. Motors are, 
however, used in so many complicated systems of wir¬ 
ing, as, for instance, in connection with printing 
presses where multi voltage control is often used and 
where motors must be reversible and capable of being 
started or stopped from different places, that the only 
■way for an operator to fit himself to deal with trou¬ 
bles on such systems is to thoroughly acquaint him¬ 
self with the details of the wiring. He should draw 
out an accurate diagram of the connections showing 
the location of every wire and learn exactly what its 
purpose is and study this diagram patiently, trying 
out what effect a short circuit at one place or a broken 
or a misplaced wire at another would have. 

By preparing himself in this manner a repairman 
can do in a few minutes what might otherwise require 
hours for, and where the loss due to an idle machine is 
figured at from ten dollars per hour upward, speed in 
locating trouble is of the utmost value. 


CHAPTER XXI 


RECORDING WATTMETERS 

To obtain a record of the amount of electrical en¬ 
ergy consumed on a circuit in a given time, it is neces¬ 
sary that some suitable form of instrument be so con¬ 
nected in the circuit that a continuous record of the 
amount of energy passing over the circuit is recorded. 
The chemical meter, a diagram of which is shown in 
Figure 182, was originally used for this purpose. This 
meter consists of zinc plates suspended in a conduct¬ 
ing solution, so arranged that a part of the total cur¬ 
rent used on the circuit passes between these plates. 
At certain intervals the plates were removed and 
weighed, the amount of metal deposited on one of the 
plates showing the amount of current used during 
the interval. 

This meter was in reality a current meter, as it did 
not take into account the variations in voltage on the 
line except, of course, as these might affect the current. 
To reduce the reading to watts it was necessary to es¬ 
timate the average voltage during the period which 
the meter was in use. Considerable work was en¬ 
tailed in the “reading” of these meters, as it was nec¬ 
essary for the meter man to carry with him enough 
plates to replace those removed and to carry back to 

30 7 


308 


Operating and Testing 


the laboratory for weighing all the plates removed. 
This type of meter had other disadvantages among 
which was the inability of the consumer to check the 
readings, and the fact that the meter could not be 
used on alternating currents; and they are now en¬ 
tirely replaced by the mechanical meters. 

It was customary when the chemical meter was in 
use, to show in the monthly statements sent to con¬ 



sumers the number of lamp hours or the number of 
ampere hours used during the period. The first me¬ 
chanical meters were simply recording ammeters and 
registered the amount of ampere hours or lamp hours. 
At the present time the wattmeter is used almost ex¬ 
clusively. 

The “watt” is the unit of electrical power and is 
the basis of all wattmeter readings. A kilowatt or 























































Recording Wattmeters 


309 


K. W. is 1,000 watts. An electrical horsepower is 
equivalent to 746 watts. For approximate calcula¬ 
tions, a horsepower is considered as equivalent to 750 
watts or % of a kilowatt; likewise a kilowatt is equal 
to 4/3 of a horsepower. A current of one ampere 
flowing through a resistance of one ohm will produce 
one watt, the E.M.F. being in this case, according to 
Ohm’s law, one volt. 

E 2 

Expressed in symbols W = IE, W = I 2 R, W = —. 

R 

An incandescent lamp taking % ampere at 110 volts, 
takes i/ 2 X HO = 55 watts. The same lamp, when 
burning, has a resistance of 220 ohms. The wattage 
is, therefore, according to the formula, W = I 2 R, 
(i/ 2 ) 2 X 220 = 55 watts. 

While the 4 ‘watt” expresses the rate at which power 
in an electrical circuit is used, it does not express the 
amount of work performed. To correctly indicate the 
actual work done, the length of time during which the 
power is acting must be taken into consideration. The 
unit of electrical work is the “watt hour, meaning 
that one watt is used for one hour. 

The distinction between a watt and a watt hour is 
similar to the distinction between the speed at which 
a train moves and the distance which it covers. To 
find the distance covered by the train we must multi¬ 
ply the speed (miles per hour) by the number of or 
fraction of an hour that the train moves at this speed 
In the same way to get the actual power consumed m 



31(J Operating and Testing 

a circuit, we must multiply the watts consumed by 
the length of time. 

An incandescent lamp taking 55 watts will, in one 
hour, require 55 watt-hours of energy. Ten such 
lamps operated for one hour would require 550 watt- 
hours ; or one such lamp operating for 10 hours would 
require 550 watt-hours. In a like manner, a liorse- 


Figure 183 

power (746 watts) in use for one hour will require 
746 watt-hours. The watt-hour is too small a unit for 
commercial purposes and the kilowatt hour, or 1,000 
watt-hours, is generally used. 

While it will be seen that there is a decided differ¬ 
ence between the terms “watt” and “watt-hour,” 
still it will be found that the two are frequently used 
synonymously, kilowatt-hours often being: referred to 















Recording Wattmeters 


311 


as kilowatts. The connection in which the term is 
used will determine the meaning. For instance, a 
monthly statement referring to so many kilowatts 
must, obviously, mean kilowatt-hours. 

The recording wattmeter, sometimes called inte¬ 
grating wattmeter, owing to the fact that it indicates 
the total watts used, consists of a small motor operated 
by the current to be measured. Figure 183 shows a 
view of the Thompson recording wattmeter and Figure 
184 a diagram of the connections. The upright shaft 





L 


Figure 184 


in the center of the meter supports the armature A, 
Figure 184. To reduce the friction to the smallest 
possible amount this shaft rests on jewel bearings. 

The coils of armature A are composed of fine wire 
which terminates in a silver commutator. Brushes, 
lightly bearing on this commutator, convey the neces¬ 
sary current to the armature. The armature, which 
is connected in series with a non-inductive resistance 
R, and the auxiliary shunt field S, is connected directly 
across the mains. The two field coils M M are wound 
















































312 


Operating and Testing 


with a rather heavy wire and connected directly in 
series with one of the mains. At the lower end of the 
shaft is a copper disk, shown in Figure 183, which ro¬ 
tates freely between the permanent magnets. A clock¬ 
work geared to the upper end of the shaft records the 
revolutions of the armature. The scheme of connec¬ 
tion is plainly shown in Figure 184. 

The armature and the shunt field S are always in cir¬ 
cuit, but as their resistance is very high the current is 
small. The tendency to turn, due to the current in 
the armature, is only affected by the voltage across the 
mains. If the two field coils were replaced by perma¬ 
nent magnets we would have in reality an instrument 
which would, with a suitable arrangement of springs 
and a pointer, serve as a voltmeter and would only 
be affected by changes in voltage across the mains. 
The two coils M M, which are connected in series with 
one of the mains, form the field in which the armature 
rotates. The greater the strength of this field, the 
greater the speed of the armature. It will therefore 
be seen that the effort which revolves the armature 
is the result of the current in the coils M M and the 
E.M.F. in the armature, the combination of these two 
being I X E or watts. 

In order that the speed of the armature may be in 
exact proportion to the watts used, a copper or alumi¬ 
num disk attached to the armature shaft is arranged 
to rotate, without touching, between a pair of perma¬ 
nent magnets. A current is generated in this disk, in 
a manner similar to that in which current is generated 
in the armature of a dynamo, and tends to retard the 
disk. The effect of this retardation is such that the 


Recording Wattmeters 


313 


rate at which the armature revolves is in exact pro¬ 
portion to the wattage used on the circuit. 

Although every effort is made to reduce the friction 
to the smallest extent possible, by providing jewel 
bearings and by making the armature, shaft and disk 
of very little weight, still it is impossible to entirely 
do away with it. Some energy, although a very small 
amount, is also required to operate the clockwork of 
the registering mechanism. The shunt field S, con¬ 
nected in series with the armature circuit, is so ar¬ 
ranged that it tends to start the armature and over¬ 
come the friction of the revolving element. The meter 
will, therefore, register on light loads and register 
more accurately at all other loads. As the torque ex¬ 
erted by the shunt field is the result of the current in 
it and that in the armature, it is evident that a change 
in the voltage across the mains will also affect the start- 
’ ing torque, the variation being proportional to the 
square of the E.M.F. The shunt field should therefore 
be adjusted for the voltage of the circuit on which it 
is to be used. 

It will be noted that the connection for the shunt 
field is made on the load side L of the meter. With 
this connection the meter will register the amount of 
current used in the armature circuit. On the other 
hand, if the connection for the shunt field circuit was 
made on the generator side of the meter it would 
receive a slightly higher pressure and take into ac¬ 
count the loss in the main coils M M. The loss in 
either case is very small. 

Meters of the Thompson type may be used with 
either direct or alternating current circuits as there 


314 


Operating and Testing 


is no iron used in their construction and the inductance 
is therefore small. Where used on alternating current 
circuits the reversals of the current in both the arma¬ 
ture and fields occur at the same time and the meter will 
continue to revolve in the one direction, for, it is well 
known, changing the direction of current in a shunt 
motor does not change the direction of rotation of the 
armature. If, however, the meter is fed from the 
wrong side it will run backward. This can readily be 
understood by referring to Figure 184. As long as 
the polarity of the supply circuit is not reversed the 
armature current remains in the same direction but 
the direction of the current through the fields depends 
upon from which side the meter is fed. 

For the measurement of power on alternating cur¬ 
rent circuits meters of the induction type possess a 
number of advantages and are used almost exclusively 
These meters are used on alternating current circuits 
only, the rotation of the revolving element being ob¬ 
tained by the joint action of a set of series coils and 
a shunt coil inducing current in a metal disk. The 
reaction of this induced current causes the armature 
to revolve in much the same way as that of an ordi¬ 
nary induction motor. As the same disk is acted upon 
by both the coils which produce the rotation and the 
permanent magnet which retards the rotation the 
weight and consequently the friction may be kept 
down to a minimum. The use of a commutator and 
its brushes are unnecessary as there is no winding on 
the revolving element. 

Figure 185 shows a view of the Guttman wattmeter 
with the dials and magnets removed. The aluminum 


Recording Wattmeters 


315 


armature which is slotted in spiral lines weighs about 
% of an ounce and rests on a jewel bearing. At the 
top of the spindle is a worm whereby the motion of the 
revolving element is transmitted to the recording 
train. The two series coils, shown directly at the left 
of the spindle, are mounted on aluminum frames. The 



Figure 185 


coils are wound with heavy wire and consume from 
two to four watts, depending on the size of the meter. 

The shunt coil of the meter is wound upon a lami¬ 
nated iron core having two air gaps, through one of 
which the disk rotates. On the lower part of this 
laminated core a heavy band of copper partially sur¬ 
rounds the iron laminations. An adjustable piece of 











316 


Operating and 'Testing 


wire is connected to the two ends of the copper band 
and completes an electrical circuit. 

In order that the meter may register accurately on 
inductive loads it is necessary that the current in the 
shunt field lag behind that of the series field by an 
angle of 90°. This will be clearly understood by con¬ 
sidering the conditions which would exist were the 
two currents in exact phase. If such was the case 
the instrument would become a recording volt-ampere 
meter and would take into account only the amperes as 
they would be indicated by an ammeter. On an induc¬ 
tive load the product of the volts and amperes does not 
represent the wattage and to obtain the true value of 
the watts the power factor must be considered. 

The greatest torque or turning moment must be ex¬ 
erted on the revolving element of the meter when the 
load is non-inductive, for then the power factor is 1 
and the product of the volts and amperes represents 
the true power. On the other hand the least torque 
should be in effect when the load is all inductive or 
when the power factor is 0, for then there is no true 
energy represented. 

In order that the current in the shunt coil may lag 
90° behind the impressed E.M.F. this coil is wound 
on the iron core to give this circuit the greatest pos¬ 
sible inductance, but as this inductance alone cannot 
produce a difference of phase of 90° other means must 
be resorted to. This is accomplished by means of the 
copper band referred to above, which, forming a closed 
circuit around this iron core, has a current induced 
in it, and this current reacting upon the field pro¬ 
duced by the shunt coil gives the effect desired. 


Recording Wattmeters 


317 


INSTALLATION OF METERS 

The manner in which a meter is connected into the 
circuit depends upon the wiring system, and the cur¬ 
rent and voltage used. Although the structural feat¬ 
ures of the various makes of meters differ the general 
scheme of connecting them into the circuit is similar. 

Figure 184 shows the Thompson meter as used on a 
two-wire circuit. Both mains are carried to the meter, 
one of them being connected to the series coil and the 



other passing through the meter by the bus bar con¬ 
nection. The shunt armature circuit is, however, con¬ 
nected to this bar. 

With large mains only one wire is carried through 
the meter, this being connected to the series coils. A 
tap taken off the other main connects to the shunt coil 
as shown in Figure 186. As this shunt tap carries 
only current for the shunt field of the meter it may be 
of small wire, generally No. 14 B. & S. gauge. 

When a meter is connected in a three-wire circuit 








































318 


Operating and Testing 


both outside mains are carried through the meter, one 
through each of the series coils. The shunt field is 
connected by means of a wire tap to the neutral main. 
The Thompson three-wire meter is shown in Figure 
187. In some types of three-wire meters no neutral 
tap is used, the shunt circuit being connected directly 
across the outside mains. This connection has an ad¬ 
vantage in that it does away with the running of one 
wire to the meter and, as the shunt field connection is 



inaccessible the possibility of tampering with the meter 
is reduced. It has, however, the disadvantage in that 
an added resistance must be placed in series with the 
shunt field when used on direct current circuits with 
the consequent increase in the power consumed by the 
meter. 

Figure 188 shows the connections for a meter on a 
balanced three phase circuit. One main is carried 
through the series coil of the meter and two taps from 
the other two main wires are carried to a common con- 




































































































Recording Wattmeters 


319 


nection through an inductive resistance and connect 
to the shunt field circuit. 

On alternating current circuits of large capacity it 
is not advisable, for several reasons, to carry the 



MTIA 

Figure 189 

mains through the meter. A small current trans¬ 
former is connected in series with one of the mains, 
the secondary of the transformer being connected to 



Figure 190 

the meter as shown in Figures 189 and 190. If the me¬ 
ter is used on a primary circuit or on any circuit where 
the voltage is high a small potential transformer may 
be connected across the mains and the shunt field con 












































320 


Operating ana Testing 


nected directly to the secondary as shown in Figures 
191 and 192. Various other combinations of both cur¬ 
rent and potential transformers are made use of; as, 
for instance, on a three-wire circuit of large capacity. 
In this case two current transformers are used, one on 
each main, the secondaries being connected to the 
series coils of the meter. 

Detailed instructions are generally sent out for the 
installation of individual meters but there are a few 



■rraa 


Figure 191 

general directions which apply to all. A meter is a 
somewhat delicate instrument and, although built to 
withstand ordinary usage, efficient operation demands 
careful and intelligent handling. As has been stated, 
the revolving element of recording wattmeters rests 
on jewel bearings. A slight jar is often all that is 
necessary to injure or break the jewel. For this rea¬ 
son acme means is always provided to remove the re¬ 
volving element from contact with the jewel when the 





























Recording Wattmeters 


321 


meter is to be carried about or during transportation, 
and the moving element should never be placed in con¬ 
tact with the jewel until the meter is ready to be 
started. 

When a meter is unpacked it should be carefully 
cleaned and examined. Some care should be exer¬ 
cised in the choice of location for setting the meter. To 
obtain the most efficient operation it should not be 
placed where it will be subject to any vibration, neither 
should it be placed in an extremely hot or cold place 
or where subject to great extremes of temperature. 



Figure 192 


Locations where dust, moisture, or inflammable or cor¬ 
rosive vapors are present should also be avoided. 

The meter should be installed in a readily accessi¬ 
ble location and should be fastened to a solid up¬ 
right support. A hole for a supporting screw is gen¬ 
erally provided at the top of the meter and a screw 
(never use a nail) should be inserted at this point 
first. The meter should then be leveled. A small 
spirit level may be used for this purpose or, where the 
meter has a disk, a small weight of some non-magnetic 
substance such as brass may be placed near the outer 





















322 


Operating and Testing 


edge of the disk. If the meter is not level the weight 
and disk will revolve to the lowest point. 

Place the weight on the front or back upper surface 
of the disk. If the disk rotates to the right or left that 
part of the meter toward which it rotates is low and 
the bottom of the meter should be moved in that di¬ 
rection. When the meter is level from right to left 
the disk and weight will not move when the weight is 
placed at the center of the disk at the front or back. 

Now place the weight on either side of the disk and 
note if the disk rotates to the front or back. If to the 
rear the back part of the meter is too low and the 
meter should be moved out at the top. If the disk ro¬ 
tates to the front that part of the meter is too low and 
should be moved out at the bottom. When a perfectly 
level position has been obtained the weight will not 
move if placed on any part of the disk It is well to 
check back after the last leveling as the first position 
may have been altered. All the screws should now be 
set up. 

The wires may now be connected to the meter, be¬ 
ing careful to follow the wiring scheme applying to 
the particular meter. The wires should be thoroughly 
cleaned and the binding posts tightly set up to avoid 
any heating at these points. Now place the revolv¬ 
ing element on its jewel if this has not already been 
done and turn on the current and note if the meter 
revolves in the proper direction. The meter case may 
now be placed on the frame, paying special attention 
to see that the case closely fits into place and no open¬ 
ing is left at the edges. 


Recording Wattmeters 


323 


TESTING 

A recording wattmeter is so designed that with a 
given wattage passing through the meter a definite 
number of revolutions of the armature will result. 
For instance, on a certain type of meter it takes 18 
seconds to complete one revolution of the armature 
on 100 watts, or 1800 seconds for one revolution on 1 
watt. This is the equivalent of 1/1800 of one revolu¬ 
tion for one seond on one watt. On this® type of meter 
the armature would require 1800 seconds to make one 
revolution while only one watt is passing through the 
meter and this is taken as the testing constant of the 
meter. To determine the wattage at any load multi¬ 
revolutions 

ply the revolutions per second, or-, by the 

seconds 

constant. As an example: Suppose the meter made 

1 

one revolution in one second, —X 1800 = 1800 watts 

1 

passing through the meter. 

In order that the same type of meter may be used 
on circuits of different voltages it is customary to in¬ 
troduce a resistance in series with the shunt circuit; 
so that no matter what voltage may be used on the 
meter the armature circuit will always have impressed 
upon it the same voltage. The number of revolutions 
of the armature will then be the same even though the 
voltage on the meter and correspondingly the wattage, 
has been increased. To make this meter indicate cor- 



324 


Operating and Testing 


rectly the train gear is altered to indicate correct 
readings. For instance, with a certain meter designed 
for use on a 110 volt circuit it requires 2000 revolutions 
of the armature to register 1000 watts. If the same 
meter was used on a 220 volt circuit, with a resistance 
in series with the shunt circuit so that the shunt cir¬ 
cuit would only receive 110 volts, the true wattage 
would be registered by arranging the gearing so that 
one revolution of the armature would produce twice 
the movement of the pointer on the dial. The testing 
constant would also be doubled. 

As meters of large capacity require a larger wire 
for the winding of the series coils, and as it is not ad¬ 
visable to run the meter at too high a speed, the field 
due to the series winding is cut down and fewer rev¬ 
olutions of the armature will result with a given load. 
In this case the train ratio and the testing constant 
are increased. 

Below are given the testing formulas for calibrating 
recording wattmeters. 

FORT WAYNE 

Rev. X 100 X Constant 

-= Watts 

Seconds 

See Instruction Book for Constants. 

WESTINGHOUSE 

Rev. X Constant 
-= Watts 


Seconds 




Recording Wattmeters 


325 


Constant = 1.2 X (Amp. X Volts as marked on 
dial). 

On types B and C, Constant = 2.4 X Amp. X Volts 
as marked on dial). 

GENERAL ELECTRIC, DUNCAN AND SCHEEFER 

Rev. X 3600 X Constant 

-— Watts 

Seconds 

G. E. Non-Direct Reading, Constant on dial. 

G. E. Direct Reading, Constant found on disk. 

Duncan, Constant on dial. (Fort Wayne Induc¬ 
tion type.) 

Duncan, Constant on disk (Direct current and S. & 
H. Induction type). 

Scheefer Non-Direct Reading, Constant on dial. 

STANLEY 

Rev. X 100 X Constant 

-= Watts 

Seconds 

Constant = Seconds required for meter to make 
revolution on 100 watts. 

Constant stamped on case. 

GUTTMAN 

Rev. X Constant 
-= Watts 


Seconds 





326 


Operating and Testing 


3600 


Constant = 


Train ratio as found on meter 


SANGAMO 


Rev. X Constant 


= Watts 


Seconds 


Constant found on back of meter. 

Any of these formulas may be rearranged for con¬ 
venience in testing. 


Revolutions X Constant 


(1) Watts 


Seconds 

Watts X Seconds 


(2) Revolutions = 


(3) Seconds — 


'4) Constant 


Constant 

Revolutions X Constant 
Watts 

Watts X Seconds 

Revolutions 
Observed secs.—Secs. 


Error = 


Secs. 


Trie testing of a wattmeter can be accomplished in 
several ways, the choice of method depending on the 









Recording Wattmeters 


327 


accuracy desired and the apparatus at hand. One of 
the simplest methods is that of turning on a number of 
16 candlepower lamps and then counting the number 
of revolutions of the meter disk in a given time. The 
load is estimated and the meter checked up by using 
the formula of the type of meter under test. As an 
example: Suppose ten 16 candlepower lamps, taking 50 
watts each, are turned on. The time required for 
one revolution according to formula (3) would be 

1 X 1800 

Seconds =-= 3.6 seconds. If the meter made 

500 




(SI 

O AS 0 vOL T MfTE* 

<^fj 

r*c~? 1 



Dm fram No I 

Figure 193 

exactly ten revolutions in 36 seconds it would be reg¬ 
istering correctly. At best this method is only ap¬ 
proximate as the wattage of the lamps must be esti¬ 
mated and this will vary considerably with different 
makes of lamps and lamps of different ages. 

To make this test more accurate a number of lamps 
may be prepared by ascertaining the watts consumed 
by each at several different voltages such as will be 
met with on the tests. These voltages and the corre¬ 
sponding wattages should be marked on labels on the 
hamps. When a meter test is made a reading should 















328 


Operating and Testing 


be taken of the voltage with a portable voltmeter and 
the exact load can then be determined. See Figure 

193. 

A regular service meter accurately calibrated in the 
shop or laboratory may be used in checking up other 
meters by connecting it in circuit as shown in Figure 

194. With the connection shown the voltage impressed 
on the shunt coils of the two meters is equalized and 
the inaccuracy which would result were the meters 
connected side by side, where the shunt coil of one 
meter would be subjected to the reduced voltage caused 


m 



t**c 


>i*« ■ >*«»«• 

|--|j 


LOAO 




> 


UlMl'Mtll 


D w |t f Nc t 

Figure 194 


by the drop in the series field of the other meter, is 
avoided. If the two meters are of the same type and 
capacity the two revolving elements will rotate in uni¬ 
son when the meter being tested is correct. If the 
meters are of different capacity this must be taken 
into account. 

The most accurate test and the one more generally 
used is shown in Figure 195. Figure 195 shows cor¬ 
rections for a standard wattmeter. The wattmeter is 
sometimes replaced by a voltmeter and ammeter. On 
direct current circuits either method may be used, but 
the wattmeter is more convenient and accurate. For 




















Recording Wattmeters 


329 


alternating currents the reading obtained by multiply¬ 
ing together the amperes and volts does not represent 
the true wattage of the circuit unless the load is non- 
inductive. For inductive loads a wattmeter must be 
used, but it is well to take both the wattmeter and the 
volt-ampere readings so that the power-factor may be 
known. 

Figure 196 shows connections for testing a three wire 
meter using one standard wattmeter. The load must 
first be balanced and the neutral fuse then opened. 



Figure 195 

This method is objectionable where the shunt coil of 
the meter under test is connected directly across the 
mains as the shunt coil of the standard wattmeter is 
subject to the variation in voltage between the neutral 
and the outside wires. To overcome this objection a 
multiplier may be used in series with the shunt coil 
of the standard meter and connection can then be made 
directly across the outside mains. If the shunt cir¬ 
cuit of the meter under test is connected between one 
of the outside mains and the neutral wire a test may be 
made by using one standard wattmeter and connecting 


















33U Operating and Testing 

up only one series coil of the meter under test at a 
time, or both series coils may be connected in series. 

The most accurate method of testing three-wire 
meters is by use of two standard wattmeters con¬ 



nected as shown in Figure 197. The sum of the stand¬ 
ard meter readings should equal the reading of the 
meter being tested. In this case it is not necessary to 
balance the load. 



It is of great importance for accurate testing that a 
good stop watch be employed, although for approxi¬ 
mate tests the second hand of the ordinary watch serves 
the purpose quite well. The longer the time of the 
test, usinsr the latter method, the less the error. 










































































KecorcLmg Wattmeters 


331 


When the apparatus is set up ready for the test, 
a small load, about 10 per cent of the full load capac¬ 
ity of the meter, is turned on. The number of revolu¬ 
tions made by the revolving element and the time over 
which the count is made are noted. By means of for¬ 
mula 1 the watts as indicated by the meter under 
test are compared with the wattage of the standard 
meter. The per cent of standard watts will be 

Meter watts X 100 

—-. Example: Suppose the revolv- 

Standard watts 

ing element made 13 revolutions in 90 seconds, the 
testing constant of the meter being 1800. Watts = 

13 X 1800 

-— = 260 watts. If the standard meter indi- 

90 

cated 250 watts the percentage of standard watts 
260 X 100 

would be -= 104 per cent, or 4 per cent 

250 

fast. 

A method frequently used, and one by which the 
percentage error may be taken direct from a previ¬ 
ously prepared table, is as follows: Ascertain the watts 
of the connected load from the reading of the standard 
wattmeter. From the following formula determine 
the number of revolutions the meter under test should 

Watts of load X 60 

make in one minute.-—-— 


Testing constant of mpfpr 






332 


Operating and Testing 


Revolutions per minute. Now note the number of sec¬ 
onds required by the meter under test to complete this 
number of revolutions. If the number of revolutions 
are completed in exactly 60 seconds, the meter is cor¬ 
rect ; if not, the meter is fast or slow. Example: On a 
load of 150 watts it is found that exactly 5 revolutions 
are completed in one minute or 60 seconds. Testing 
constant of meter is 1800. According to formula 2 


150 X 60 

Revolutions =-= 5. If this meter had com 

1800 


60 X 100 

pleted 5 revolutions in 55 seconds it would be- 

55 


= 109.09 per cent, or 9.09 per cent fast. If five rev¬ 
olutions had been completed in 67.8 seconds, it would 

60 X 100 

be-= 88.5 per cent, or 11.5 per cent slow. 

67.8 

The following table gives the per cent of error for 
time in fifths of a second. 





Recording Wattmeters 


333 


PER CENT ERROR TABLE FOR FIFTHS OF A SECOND. 


Time in 
Seconds 

Per Cent 
Fast 

Time in 

Seconds 

Per Cent 
Fast 

40.20 

49.25 

50.20 

19.52 

.40 

48.51 

.40 

19.05 

.GO 

47.78 

.60 

18.58 

.80 

47.06 

.80 

18.11 

41.00 

46.34 

51.00 

17.65 

.20 

45.63 

.20 

17.19 

.40 

44.93 

.40 

16.73 

.60 

44.23 

.60 

16.28 

.80 

43.54 

.80 

15.83 

42.00 

42.86 

52.00 

15.38 

.20 

42.18 

.20 

14.94 

.40 

41.51 

.40 

14.50 

.60 

40.85 

.60 

14.07 

.80 

40.19 

.80 

13.64 

43.00 

39.53 

53.00 

13.21 

.20 | 

38.89 

.20 

12.78 

.40 

38.25 

.40 

12.36 

.60 

37.61 

.60 

11.94 

.80 

36.98 

.80 

11.52 

44.00 

36.36 

' 54.00 

11.11 

.20 

35.75 

.20 

10.70 

.40 

35.14 

.40 

10.29 

.60 

34.53 

.60 

9.89 

.80 

33.93 

.80 

9.49 

45.00 

33.33 

55.00 

9.09 

.20 

32.74 

.20 

8.69 

. 40 # 

32.16 

.40 

8.30 

.60 

31.58 

.60 

7.91 

.80 

31.00 

.80 

7.53 

46.00 

30.43 

56.00 

7.14 

.20 

29.87 

.20 

6.76 

.40 

29.31 

.40 

6.38 

.60 

28.76 

.60 

6.01 

.80 

28.21 

.80 

5.63 

47.00 

27.66 

57.00 

5.26 

.20 

27.12 

.20 

4.89 

.40 

26.58 

.40 

4.53 

.60 

26.05 

.60 

4.17 

.80 

25.52 

.80 

3.81 

48.00 

25.00 

58.00 

3.45 

.20 

24.40 

.20 

3.09 

.40 

23.96 

.40 

2.74 

.60 

23.45 

.60 

2.39 

.80 

23.15 

.80 

2.04 

49.00 

22.45 

59.00 

1.69 

.20 

21.95 

.20 

1.35 

.40 

21.46 

.40 

1.01 

.60 

20.97 

.60 

0.67 

.80 

20.48 

| .80 

0.33 

50.00 

20.00 

| 60.00 

0.00 


Time in 
Seconds 

Per Cent 
Slow 

Time in 
Seconds 

Per Cent 
Slow 

60.20 

0.33 | 

70.20 


14.52 

.40 

0.67 

.40 


14.77 

.60 

0.99 

.60 


15.01 

.80 

1.31 

.80 


15.25 

61.00 

1.63 

71.00 


15.50 

.20 

1.96 

.20 


15.73 

.40 

2.27 

.40 


15.96 

. 6 i > 

2.59 

.60 


16.20 

.80 

2.91 

.80 


16.43 

62.00 

3.22 

72.00 


16.66 

.20 

3.53 

.20 


16.89 

.40 

3.84 

.40 


17.12 

.00 

4.15 

.60 


17.35 

.80 

4.45 

.80 


17.58 

63.00 

4.76 

73.00 


17.81 

.20 

5.06 

.20 


18.03 

.40 

5.36 

.40 


18.25 

.60 

5.66 

.60 


18.47 

.80 

5.95 

.80 


18.70 

64.00 

6.25 

74.00 


18.92 

.20 

6.54 

.20 


19.14 

.40 

6.83 

.40 


19.35 

.60 

7.12 

.60 


19.57 

.80 

7.40 

.80 


19.79 

65.00 

7.69 

75.00 


20.00 

.20 

7.97 

.20 


20.21 

.40 

8.25 

.40 


20.42 

.60 

8.53 

.60 


20.63 

.80 

8.81 

.80 


20.84 

66.00 

9.09 

76.00 


21.05 

.20 

9.36 

.20 


21.26 

.40 

9.63 

.40 


21.47 

.60 

9.90 

.60 


21.68 

.80 

10.17 

.80 


21.88 

67.00 

10.44 

77.00 


22.08 

.20 

10.71 

.20 


22.28 

.40 

10.97 

.40 


22.38 

.60 

11.24 

.60 


22.68 

.80 

11.50 

.80 


22.88 

68.00 

11.76 

78.00 


23.08 

.20 

12.02 

.20 


23.28 

.40 

12.28 

.40 


23.47 

.60 

12.53 

.60 


23.66 

.80 

12.79 

.80 


23.86 

69.00 

13.04 

79.00 


24.05 

.20 

13.29 

.20 


24.24 

.40 

13.54 

.40 


24.43 

.60 

13.79 

.60 


24.63 

.80 

14.04 

.80 


24.82 

70.00 

14.28 

80.00 


25.00 


The per cent of full load on which tests should be 
made will vary with the class of work on which the 
meter is used. Where the load connected to the meter 
is such that it will be used uniformly over the range of 





































334 


Operating and Testing 


the meter tests should be made at 10 per cent, 20 per 
cent, 30 per cent, etc., (10 per cent intervals) over the 
full range of the meter. On the other hand, if the load 
is such that only the full load connected to the meter 
is used, such as on an electric sign, more tests should 
be made at the full load capacity. On the ordinary 
residence load a test at 4 per cent and 100 per cent of 
full load will generally suffice. 

Meters carrying large loads should be tested every 
30 days. If the meter is placed where there is much 
jarring it will tend to run fast. 

All meters have a tendency to gain in speed because 
of the gradual weakening of the controlling magnets. 

Commutator troubles are the greatest source of in¬ 
accuracies of meters. Some operators insert small 
fuses in armature circuit. This is especially useful 
when there is danger from lightning. 

READING OF METERS 

As has been previously stated, the basis of all re¬ 
cording wattmeter readings is the kilo-watt hour, the 
equivalent of one kilowatt used for one hour. It is 
not necessary that exactly a kilowatt of current be 
used, or that the current be used for the exact period 
of one hour, but that the product of the watts and the 
hours shall equal 1000 watt-hours. For instance: A 
16 candlepower lamp taking 50 watts and burning for 
20 hours represents one kilo-watt hour. Twenty of 
these 50 watt lamps burning for a period of one hour 
also represent one kilo-watt hour. 

Meter readings are indicated by the positions of 
pointers which move over a number of dials as shown 


Recording Wattmeters 


335 


in Figure 198, the difference between any two readings 
representing the amount of power used during the 
interval between these readings. The pointers shown 
on the dials in Figure 198 are so connected by means 
of clockwork that a total revolution of any pointer 
represents l/10th of a revolution of the pointer to 
the left of it. It will also be noted that each dial 
reads in opposite directions to the one next to it. 

At the top of the individual dials the value of the 
reading of that dial is shown. Wliere the figures given 
are followed by the letter “s” it signifies that each 
division of the dial represents the amount of current 
indicated by the figure at the top. For instance, in 
Figure 200 each division of the dial at the right rep¬ 
resents l/10th of one kilowatt and a total revolution 
of the dial 10/10ths or 1 kilowatt. In a like manner, 
each division of the second dial from the right repre¬ 
sents 1 kilowatt and a total revolution of the pointer 
on this dial, 10 kilowatts. 

If the figure given at the top of the dial is not fol¬ 
lowed by the letter “s”, or as shown in Figure 199, 
each division of the dial represents l/10th of the 
amount shown at the top of the dial, the dial at the 
right of Figure 199 indicating 9/10ths of 10 kilowatts 
or 9 kilowatts. 

The reading of a meter should always be from right 
(lowest dial) to left, each reading of the dial at the 
left being used as a check on the reading of the dial 
at the left. The following examples will make clear 
the manner of reading meters: 

In Figure 198 the right hand pointer registers 
9/10ths of 1000 watt hours or 900 watt hours r - the 


336 


Operating and Testing 


pointer next to it registers 8 (it cannot have passed 
the figure 9 as the pointer on the dial at the left of it 
has not made a complete revolution) ; the middle dial 



Figure 198 


also registers 8; as the middle pointer has not passed 
the 0, the 4th dial must be read 1; the last dial also 



indicates 1, making the total reading 1,188,900 watt 
hours. 

In Figure 199 the readings on the meter dial are 











Recording Wattmeters 


337 


shown in kilowatt hours. The first pointer at the right 
reads 9; as this pointer has not passed the 0 mark, the 
dial to the left must be read 8; each of the remaining 



hours. 

In Figure 200 the readings are also given in kilo¬ 
watt hours. The pointer on the first dial at the right 



Figure 201 


has not passed the 0 mark so this dial must be read 
9/lOtlis of a kilowatt hour or .9; the second dial reads 
5 ; the middle dial 6; the fourth dial 9 and the last 
dial 1, making the total reading 1965.9 kilowatt hours. 
In Figure 201 the dial at the right indicates 9 kilo- 









338 


Operating and Testing 


watt hours; the second dial 9; the third 4, and the 
fourth 9, making a total reading of 9499 kilowatt 
hours. 

On some types of meters a multiplier is used. This 
is generally given on the meter dial and the readings 
as indicated by the pointers should be multiplied by 
this number to obtain the correct reading of the meter. 

DISCOUNT METER 

Figure 202 shows a diagram of what is known as the 
Wright discount or demand meter. This meter is 



used on circuits where it is desired to know the maxi¬ 
mum current which has passed through the circuit. 
In the diagram, B is a glass bulb connected to a tube 
U which is partly filled with a liquid. Around bulb 
B is wound a resistance wire which carries the main 
current. When current flows in this wire heat is 
generated and the air in the bulb is expanded, thus 
forcing the liquid around tube U until it reaches the 
point where tube TJ and I join, when it will flow into 










Recording Wattmeters 


33 y 



• CALK OF DISCOUNT METER 

Figure 203 


tube I. The amount of liquid in tube I will depend 
upon the maximum current which has passed through 
the resistance wire on bulb B. The meter is not af- 









340 


Operating and Testing 


fected by momentary increases in current. If the 
maximum current lasts five minutes, 80 per cent will 
register; ten minutes, 95 per cent will register ; thirty 
minutes, 100 per cent will register. Figure 203 shows 
the scale of this- meter. The left-hand scale shows the 
maximum current used in amperes and the right-hand 
scale the kilowatt hours for which the customer must 
pay full rate. 

As. a discount meter, this meter is connected in se¬ 
ries with one of the mains connecting to the ordinary 
recording wattmeter. On three-wire circuits a dis¬ 
count meter must be connected in each main, this re¬ 
quiring two meters. As the scale is computed for 115 
volt circuits, when the meter is used on a 230 volt cir¬ 
cuit the reading must be doubled, as indicated at the 
bottom of the scale. 

The recording wattmeter registers the total con¬ 
sumption of energy and the discount meter the pro¬ 
portion of it to be charged at full rate. The excess 
of the recording wattmeter reading over the discount 
meter reading is subject to the lower rates as specified 
by the lighting company. In case the wattmeter read¬ 
ing is less than the discount meter reading only the 
consumption as shown by the recording wattmeter is 
charged at the full rate. 

The discount meter shows the full rate portion of 
the bill for one month of 30 days. When computing a 
bill for a greater or less time the reading should be 
proportioned according to the time. After each 
monthly reading the meter is opened and the tube 
tipped up until all the liquid flows out. If there is 
current in the meter, the liquid will flow back again 


Recording Wattmeters 


341 


when the tube is turned down; otherwise the tube will 
remain empty until current is used. 

The purpose for which this discount meter is used 
is to obtain a more equitable basis for the charge for 
current. As practically all users of current, for light¬ 
ing for instance, use the maximum amount of current 
at the same time, the cost to the lighting companies of 
both the generation of this current and transmission of 
it to the consumer is a maximum at this time. They 
must have sufficient generating apparatus and trans¬ 
mission lines to supply the demand and the line losses 
at this time are considerably greater. This extra 
equipment must be maintained for the short interval 
during which this extra demand is made, or at the 
peak of the load. 

It is assumed that a consumer will use the maximum 
amount of current for one hour each day during the 
thirty days of the month, and the kilowatt hours to be 
paid for at full rate are computed on this basis. Sup¬ 
pose a current of ten amperes was indicated by the 
maximum meter as the greatest amount of current 
used during the month. Ten amperes at llo volts 
amounts to 1150 watts, and this amount used for 
one hour a day for 30 days represents 30 X H50 
— 34,500 watt-liours or 34.5 kilowatt-hours as the 
amount of current to be paid for at the full rate. 
An examination of the meter scale as shown in Figure 
22 will show that a current of ten amperes is equiva¬ 
lent to 34.5 kilowatt-hours at the full rate. 


CHAPTER XXII 


LIFE AND FIRE HAZARD 

Electricity may endanger life or seriously maim in 
tfwo ways: By direct contact, causing severe shock and 
often instant death, and by burning through the me¬ 
dium of a flash or arc which may also prove destruc¬ 
tive to the eyesight. 

A shock may be obtained by touching wflres of oppo¬ 
site polarity; by touching one wire and making con¬ 
nection to the ground, the other wire being grounded, 
or by cutting one’s self into the circuit. 

It is perfectly safe to touch any one bare wire pro¬ 
vided one is perfectly insulated from the ground, and 
even if one is not insulated, if the wires are clear from 
the ground no harm will be done, but under no circum¬ 
stances should one ever trust a system of wiring, a 
ground may come on at any moment and cause instant 
death. The general rule for handling live wires of 
high potential is, to use only one hand at a time and 
keep well insulated from the ground and from wires of 
opposite polarity. 

While working on dead lines that are connected with 
stations over which the workman has no control and 
which may be connected up by mistake at any moment, 
it is a good plan to short circuit those wires and 
ground them. If now the station attendant should 


342 


Life and Fire Hazard 343 

throw in switches no harm would be done except to 
his fuses 

Whenever it is necessary to cut wires carrying cur¬ 
rent, they should be merely cut into a little with the 
pliers (to cut clear through will burn the pliers) and 
then the wire may be broken, but under no circum¬ 
stances should one bridge the cut with arms or hands. 
The breaking of the circuit will produce an enormous 
voltage for an instant which may be amply sufficient 
to cause death to any one holding the ends of a broken 
wire. If a high potential circuit is to be broken in 
this way it is best to work the wire in two with a stick. 

The severity of a shock obtained from a circuit will 
depend upon the voltage of the circuit, the degree of 
contact the person makes with the wires, the condition 
of the body where it touches, whether moist or dry, 
and the quality of the ground which may be helping to 
make the circuit through the body. Thus it is by no 
means always safe to touch a live wire of 200 volts nor 
always fatal to receive a shock from 2000 volts. 

Many people have been killed by the lower voltage 
and many have escaped unharmed from shocks ob¬ 
tained from the higher pressure. 

The greatest danger to the eyesight and from burns 
is encountered while fusing up or throwing in switches 
on circuits carrying heavy currents. Many switches 
are built so that the handle is directly above the fuses. 
In case such a switch is thrown in while there is a 
short circuit on the line the operator’s hands are likely 
to be burned very badly. It is best to cover the fuses 
with asbestos or to procure a stick with which the 
switch may be pushed in. 


344 


Operating and Testing 


Where circuits are controlled by circuit breakers 
there should always be a switch which must be open 
until the breaker is set so that the hand may not inter¬ 
fere if the breaker should start to go out at once be¬ 
cause of overload or short circuit. 

To install fuses in a live circuit which cannot be 
disconnected by switches is always a matter attended 
with some risk. As a rule the nature of the “blow” 



Figure 204 


% 


will give some idea as to whether it was caused by an 
overload or a short circuit. The current due to a short 
circuit will generally be many times greater than that 
of an overload owing to the fact that it requires some 
time for the fuse to heat. If there is indication that 
Miere is a short circuit, tests had better be made before 
attempting to install the proper fuses. A circuit sup¬ 
plying a large number of lights cannot be tested for 

























Life and Fire Hazard 


345 


‘‘short” in the ordinary manner because the lights 
establish a circuit of low resistance. If both fuses are 
out, the best way to test it is, by connecting a s.iiall 
fuse into the circuit, trying one side of the fuse block 
at a time. If there should happen to be two grounds, 
as at H and K, Figure 204, a fuse installed at 1 will 
not blow, but placed in 2 it will. If each side singly 
holds a small fuse without blowing, a fuse of the 
proper size may be safely installed on one side. When 
this is done a piece of wire of suitable size may be 
fastened to one of the terminals on the opposite side 
and this wire used to bridge the other fuse gap The 
wire should be of such a length that the workman need 
not endanger his eyes or hands while making connec¬ 
tion. If the fuses in question are very large the first 
fuse may be covered with asbestos. If the first fuse 
does not blow when the circuit is completed with the 
wire (known as a “ jumper”) the second may be in¬ 
stalled, leaving the wire to carry the current until 
the fuse is in place. 

The fire hazard of electric wiring consists in the 
possibility of overheating wires when carrying too 
much current; where circuits are broken an arc is 
always established which may communicate fii e; 
where wires come in contact with wood moisture may 
cause a ground along which current may flow, event¬ 
ually charring the wood and starting a fire; wires may 
come in contact with gas pipes and gradually, by mak¬ 
ing intermittent contact, eat holes into the pipe, al¬ 
lowing gas to escape which finally is fired by the 

spark. 

Lamps and motors may also become so much over- 


346 


Operating and Testing 


heated as to communicate fire to combustible material. 
Many fires are also caused by small sparks as from 
switches and sockets setting fire to gases or lint in 
factories. 

An incandescent lamp ordinarily does not become 
very hot but when covered over with paper or cloth 
or when subject to an abnormal voltage it may easily 
cause fires. Many of them have done so. 


CHAPTER XXIIT 


GROUND DETECTORS AND LIGHTNING ARRESTERS 


As a rule all systems of wiring should be kept free 
from grounds. The exceptions to this rule are three- 
wire systems of such magnitude that it becomes prac¬ 
tically impossible to do so, and in such cases the neutral 

wire is permanently grounded. 

In some cases it may be advisable to install groun . 
detectors that give continuous indications, but as such 
indicators introduce a permanent ground which un¬ 
der favorable circumstances becomes an aid in break¬ 
ing down the insulation of the opposite polarity from 
the one to which it is attached, this is not generally de- 


Either of the lamp systems of ground detectors here 
described can be made continusuoly indicating by per¬ 
manently closing the switch which connects the lamps 
to ground and voltmeters may be used in place of ie 

Figure 205 is the simplest and cheapest of all 
ground detectors. Only two lamps and a push button 
are required. As long as the lamps are not connected 

to the ground, they burn in series at about half cam 
dlepower. If the switch is kept closed and a ground 
occurs on one side of the system, the lamp on that side 

347 


348 


Operating and Testing 


burns dull and the other becomes brighter. If the 
ground is very “good,” the lamp on the side of the 
ground will be entirely extinguished and the other will 
be at full candlepower. 

Figure 206 shows method of using voltmeter as 



Figure 205 Figure 206 


ground detector. The lamps shown above are not very 
sensitive and will not indicate a slight ground. Hence 
the voltmeter is preferable. As long as both buttons 
are in their normal position, the voltmeter measures 
the voltage of the system. By pressing down either 



button, if a deflection is obtained, it indicates a ground 
on that side of the system to which the button belongs. 

Figure 207 shows ground detector connections using 
lamps for an ordinary three-wire or three-phase sys¬ 
tem. Used in connection with the ordinary three-wire 



























Ground Detectors and Lightning Arresters 349 

system, no indication will be obtained while the s\v itch 
JS connected to the leg that is grounded. If one leg is 
grounded the lamps will be either at full or half can- 
dlepower, depending upon which leg the switch is 

nlaced. 

With three-phase systems, also, no indication will be 
obtained as long as the switch is connected to the 
grounded leg. When it is connected to the other legs 

the lamps will bum bright. 

Another ground detector for three-phase systems is 

shown in Figure 208. 



MM 



Figure 208 


With this connection as long as the line is clear the 
two voltmeters show even pressure. With a ground 
coming on one side, say at X, voltmeter 1 will read 
lower and 2 higher; with a ground on the opposite side 
2 will read low and 1 high. With a ground on the mid¬ 
dle wire, both will read higher. 

Ground detectors like the above are reliable only if 
one side of the system is clear. The ground on any 
side acts as a shunt to the lamp on that side and if such 
shunts exist on both sides, it is clear that the indica¬ 
tions will be confusing. Tests should, therefore, be 
frequently made so as to be reasonably sure that a 
ground will be detected as soon as it comes on. 



















350 


Operating and Testing 


If a system is to have a thorough test, it must be 
disconnected and tested with a Wheatstone bridge or 
other method described elsewhere. 

LIGHTNING ARRESTERS 

A lightning discharge takes place only in obedience 
to an enormous pressure and is of very short duration. 
During this exceedingly short time the counter E.M.F. 
of magnets and other inductive arrangements is so 


M 



Figure 209 


great that it is easier for the current to jump a small 
air gap than force its way over an ordinary transmis¬ 
sion line. 

The simplest form of lightning arrester is shown in 
Figure 209. When the discharge occurs, the current 
jumps the spark gap between the two metal plates M. 
If these are connected to a dynamo circuit carrying 
much current, the arc established by the lightning dis¬ 
charge will be maintained by the dynamo and the re¬ 
sult will be a short circuit. This type of arrester can. 







Ground Detectors and Lightning Arresters 351 


therefore, be used only in connection with circuits such 
as telegraph or telephone in which the currents are not 
of sufficient strength to maintain an arc. 

A single plate of this kind is also useful if mounted 
closely to belts which give trouble from static charges. 

The best known type of lightning arrester is that 
of Prof. Thomson. In this, the arc which is established 
by the discharge, is immediately blown out magnetic¬ 
ally by the dynamo current. Entering at L, Figure 


@ 0 ® 


Figure 210 Figure 211 

210, the lightning jumps the gap G and passes to 
ground. The magnetism existing in the coil forces 
the arc upward until it breaks It is essential that 
this arrester be so connected that the side L is toward 
the outside lines. 

Another form of lightning arrester is illustrated in 
Figure 211. This form is used with alternating cur¬ 
rent circuits only. It consists of three cylinders placed 
very close together as shown. These cylinders may be 
of non-arcing metal, and besides offer such a large sur- 





























352 


Operating and Testing 


face over which the arc spreads that it does not create 
a high enough temperature to maintain itself. Ordi¬ 
narily only a very small spark is noticed. 

For use with high voltages either of the foregoing 
forms may be connected in series. Each wire leading 
overhead to the outside should be protected. The 
ground wire for lightning arresters should be as 
straight as possible; should be of copper, never of iron 
and should not be run in proximity to iron. 


INDEX 


Accumulators . 

Acme testing set .-. 

Alternating current . 

Alternating current motors . 

Alternating current motors, types of. 

Alternators, operation of . 

Ammeters .* * * 

Ampere . 

Ampere turns . 

Arc dynamo . 

Arc dynamo, starting of. 

Arc lamps .. 

Arc lamps on alternating current circuits 

Armature, heating of . 

Auto-starter . 

Balancing set . 

Batteries, primary . 

Battery rooms . 

Belts . 

Booster . 

Brush arc dynamo . 

Brushes, shifting of . 

Candlepower of arc . 

Candlepower, test for . 

Carbons for arc lamps . 

Charging storage batteries . 

Circuit testing . 

Circular millage of wires . 

Closed circuit batteries . 

Compass needle . 

Commutator . 

Compensator . 


Page 

... 114 : 

...262 
. 44-68 
86-148 
...96 
...124 
...255 
...15 
, .26-28 
.. 60 
...106 
...184 
...187 
, ...301 

_149 

....120 
....170 

_176 

. . . . 102 
.. . .177 

_ 60 

.... 53 
....192 
....291 

_188 

. . . .177 
....275 

_286 

_172 

_245 

_ 44 

.120 


































Index 


Compound wound dynamo . 65 

Compound wound dynamos in parallel.114 

Compound wound motors. 84 

Condensers . 31 

Conductivity of metals . 12 

Cooper Hewitt lamps .240 

Coulomb . 16 

Counter—electromotive of motors . 76 

Cross currents .128 

Delta connected transformers .163 

Delta connected armature .100 

Differential arc lamp .200 

Differential wound motor . 85 

Direction of flow of current . 8 

Direction of flow of induced current. 40 

Discount meter .338 

Distribution of light from incandescent lamps.235 

Drum armatures . 47 

Dynamo-electric machines . 39 

Dynamos, operation of direct current.102 

Dynamos, testing of .269 

Dynamo troubles .298 

Dynamos, types of . 56 

Efficiency of dynamos .270 

Efficiency of incandescent lamps.219 

Efficiency of motors .270 

Efficiency of transformers .167 

Equalizer wires .114 

Enclosed arc .193 

Electric current . 7 

Electric induction .153 

Electrolysis, testing for . . ..287 

Electrolyte for storage batteries .175 

Electromagnets, heating of . 36 

Electromagnets, winding of . 35 

Electro-magnetic induction. 42 

Electromotive force . 7 

Farad . 16 








































Index 

4 

Field magnet. 39 

Fixture testing .283 

Flaming arc . 205 

Foucault currents . 157 

Galvanometer, tangent .246 

Galvanometer, mirror.248 

Gramme ring armature . 47 

Gravity cell . 172 

Ground detector .. 347 

Grounding, dynamo frames.107 

Grounding, transformers .167 

Grounds, testing for. 275-347 

Henry . 18 

High potentials, handling of.168 

Hysterisis . 33 

Illumination from arc lamps...194 

Illumination from incandescent lamps.234 

Incandescent lamps . 217 

Incandescent lamps, efficiency of, with variation in volt¬ 
age .223 

Induced currents . 10 

Induction motors . 90 

Installation of meters.317 

Instruments for testing .243 

Insulation resistance, testing for, with voltmeter.270 

Insulators . 12 

Joule . 17 

Kilowatt . 308 

Laminating cores.33-157 

Leclanche batteries.173 

Life and fire hazard.342 

Life of incandescent lamps. 224 

Lightning arresters .350 

Lines of force. 21-24 

Loss, testing for. 284 

Magnets .*.265 

Magnets, bar . 20 

Magnets, electro . 23 







































Index 


Magnetic flux. 

Magnetism . 

Magnetomotive force . 

Maximum demand meter. 

Mirror galvanometer . 

Mercury arc lamp.. 

Mercury arc rectifier. 

Mercury rectifier for arc lamps. 

Mesh winding, armature. 

Metallized filament lamp. 

Meter, discount . 

Meter, installing. 

Meter reading . 

Meter, testing of. 

Meter, three-phase . 

Meter, three-wire .. 

Motor troubles . 

Motors, alternating current.. 

Motors, direct current . 

Motors, operation of. 

Motors, testing of. 

Motors, three-phase .. 

Motors, types of, direct current. 

Multiple arc.. 

Mutual induction . 

Nernst lamps. 

Neutral point . 

No-voltage release . 

Ohm . 

Open circuit battery . 

Open circuit, test for. 

Operation of arc lamps. . .. 

Overload release . 

Parallel circuits . 

Parallel operation of alternators. 

Parallel operation of direct current dynamos 

Photometry .. 

Polarity, testing for dynamos. 


. . . . 19 
.... 25 
....338 
....248 
. ...240 
. . . .180 
....215 
. . . .100 
. ...230 
.. . .338 
, ...317 
. ...334 
...323 
, ...318 
. ...318 
, ...302 
,...148 
,. .. 74 
... 145 
...269 
, ...149 
, . . . 80 
. . . .196 
.. . .155 
....239 
.. .. 53 
.. . .145 
.... 14 
....172 
....278 
....207 
....145 
.... 11 
....126 
....112 
....291 
109-116 








































Index 


polarized magnet . 

Power factor .. 

Primary battery . 

Prony brake . 

Racing of motors. 

Range of carbons.... 

Rating of arc lamps. 

Rating of incandescent lamps. 

Reading of meters..' 

Recording wattmeters . 

Rectifier, for alternating current dynamos 

Rectifier, for arc lamps. 

Rectifier, mercury arc.... 

Regulator, series arc. 

Resistance, magnetic . 

Reversing alternating current motors.... 

Rheostat, field . 

Rheostat, starting... 

Ring armature. 

Rotary converter, operation of. 

Rotor... 

Series arc . 

Series arc switchboard.-• 

Series circuit . 

Series dynamo. 

Series motor . 

Series operation of arc machines. 

Shunt dynamo. 

Shunt dynamos in parallel. 

Shunt dynamos, starting of. 

Shunt for ammeter.. 

Shunt motor . 

Slip of induction motor.. 

Smashing point of incandescent lamps.. 

Solenoid . 

Sparking of brushes. 

Squirrel cage armature. 

Star connected transformer. 


.. 32 
. .133 
. .170 
. .273 
, . .304 
. . .188 
. ..191 
...221 
.. .334 
. ..307 
71-124 
. . .215 
.. .180 
...214 
...26 
. . .15C 

. . .145 
...47 
. . .133 
,... 95 
....196 
....211 
. . .. 11 
.... 56 
.... 80 
....109 
.... 63 
.. . .112 
....111 
....256 
.... 83 
.... 94 
.. . .225 

. 30 

.299-304 

. 94 

.163 








































Index 


Star winding, armature. 100 

Starting box, automatic.145 

Stator . 95 

Step-down transformer .152 

Step-up transformer . 152 

Stillwell regulator .133 

Storage batteries .174 

Switchboard, charging storage batteries.178 

Switchboard, series arc. 211 

Synchronizing alternators .126-130-134 

Synchronous motors. 89 

Synchroscope, Lincoln . 139 

Tangent galvanometer.246 

Tantalum lamp .231 

Telephone receiver for testing.266 

Testing, arc lamps.210 

Testing, carbons .188 

Testing, circuits .275 

Testing, connections on interior wiring.282 

Testing, dynamos and motors. 269 

Testing, electrolysis . 289 

Testing, fixtures .283 

Testing, incandescent circuits.279 

Testing, instruments for.243 

Testing, for loss.284 

Testing, meters .323 

Testing, polarity .129-281 

Testing, rail bonds.291 

Testing, transformers .165 

Thomson wattmeters.311 

Thomson-Houston dynamo . 62 

Thomson-Houston arc switchboard.211 

Three-phase transformer connections.164 

Three-wire systems . 184 

Three-wire transformers .161 

Transformers . 151 

Transformer connections.159 

Transformers in parallel.162 








































Index 


Trimming arc lamps . 
Tungsten lamps .... 
Two-wire meters .. . 

Volt . 

Volt, production of.. 

Voltmeter . 

Watt . 

Watt-hour . 

Wattmeter, recording 
Weston instruments 
Wheatstone bridge .. 


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.255 
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